diff --git a/README.md b/README.md
index 4124e9a..f7aeb5c 100644
--- a/README.md
+++ b/README.md
@@ -3,7 +3,7 @@
 
 Elixir implementation of [Chargebee API](https://apidocs.chargebee.com/docs/api).
 
-## v0.1.4
+## v0.2.0
 This is a work in progress: right now, we only implement those methods:
 - list
 - retrieve
@@ -11,18 +11,22 @@ This is a work in progress: right now, we only implement those methods:
 
 on those resources:
 - addon
+- coupon_code
+- coupon_set
 - customer
+- event
+- gift
 - hosted_page
-  - also checkout_new
-  - also checkout_existing
-- subscription
-  - also create_for_customer
+- invoice
+- item_family
+- item_price
+- item
+- payment_intent
+- payment_source
 - plan
 - portal_session
 - subscription
-- invoice
-  - also close
-  - also import_invoice
+
 
 ## Installation
 The package can be installed by adding `chargebee_elixir` to your list of dependencies in `mix.exs`:
@@ -30,7 +34,7 @@ The package can be installed by adding `chargebee_elixir` to your list of depend
 ```elixir
 def deps do
   [
-    {:chargebee_elixir, "~> 0.1.4"}
+    {:chargebee_elixir, "~> 0.2.0"}
   ]
 end
 ```
diff --git a/config/config.exs b/config/config.exs
index c82c5f9..6570450 100644
--- a/config/config.exs
+++ b/config/config.exs
@@ -5,7 +5,7 @@
 # is restricted to this project.
 
 # General application configuration
-use Mix.Config
+import Config
 
 # Import environment specific config. This must remain at the bottom
 # of this file so it overrides the configuration defined above.
diff --git a/config/dev.exs b/config/dev.exs
index d2d855e..becde76 100644
--- a/config/dev.exs
+++ b/config/dev.exs
@@ -1 +1 @@
-use Mix.Config
+import Config
diff --git a/config/test.exs b/config/test.exs
index a13f4a0..b632b79 100644
--- a/config/test.exs
+++ b/config/test.exs
@@ -1,4 +1,4 @@
-use Mix.Config
+import Config
 
 config :chargebee_elixir,
   namespace: "test-namespace",
diff --git a/lib/chargebee_elixir.ex b/lib/chargebee_elixir.ex
index 94d97e2..279c569 100644
--- a/lib/chargebee_elixir.ex
+++ b/lib/chargebee_elixir.ex
@@ -1,3 +1,5 @@
 defmodule ChargebeeElixir do
-
+  @moduledoc """
+  Resources for interacting with Chargebee API Resources
+  """
 end
diff --git a/lib/chargebee_elixir/addon.ex b/lib/chargebee_elixir/addon.ex
index eece7f7..afe20b0 100644
--- a/lib/chargebee_elixir/addon.ex
+++ b/lib/chargebee_elixir/addon.ex
@@ -1,3 +1,6 @@
 defmodule ChargebeeElixir.Addon do
+  @moduledoc """
+  an interface for interacting with Addons
+  """
   use ChargebeeElixir.Resource, "addon"
 end
diff --git a/lib/chargebee_elixir/coupon.ex b/lib/chargebee_elixir/coupon.ex
new file mode 100644
index 0000000..afb66f4
--- /dev/null
+++ b/lib/chargebee_elixir/coupon.ex
@@ -0,0 +1,26 @@
+defmodule ChargebeeElixir.Coupon do
+  @moduledoc """
+  an interface for interacting with Coupons
+  """
+  use ChargebeeElixir.Resource, "coupon"
+
+  def create_for_items(params) do
+    create(params, "/create_for_items")
+  end
+
+  def update_for_items(coupon_id, params) do
+    post_resource(coupon_id, "/update_for_items", params)
+  end
+
+  def delete(coupon_id) do
+    post_resource(coupon_id, "/delete", %{})
+  end
+
+  def copy(coupon_id, params) do
+    post_resource(coupon_id, "/copy", params)
+  end
+
+  def unarchive(coupon_id) do
+    post_resource(coupon_id, "/unarchive", %{})
+  end
+end
diff --git a/lib/chargebee_elixir/coupon_code.ex b/lib/chargebee_elixir/coupon_code.ex
new file mode 100644
index 0000000..3494908
--- /dev/null
+++ b/lib/chargebee_elixir/coupon_code.ex
@@ -0,0 +1,14 @@
+defmodule ChargebeeElixir.CouponCode do
+  @moduledoc """
+  an interface for interacting with Coupon Codes
+
+  Supports:
+   - List
+   - Retrieve
+  """
+  use ChargebeeElixir.Resource, "coupon_code"
+
+  def archive(coupon_code) do
+    post_resource(coupon_code, "/archive", %{})
+  end
+end
diff --git a/lib/chargebee_elixir/coupon_set.ex b/lib/chargebee_elixir/coupon_set.ex
new file mode 100644
index 0000000..08cf49c
--- /dev/null
+++ b/lib/chargebee_elixir/coupon_set.ex
@@ -0,0 +1,24 @@
+defmodule ChargebeeElixir.CouponSet do
+  @moduledoc """
+  an interface for interacting with Coupon Sets
+
+  Supports
+   - List
+   - Retrieve
+   - Create
+   - Update
+  """
+  use ChargebeeElixir.Resource, "coupon_set"
+
+  def add_coupon_codes(coupon_id, params) do
+    post_resource(coupon_id, "/add_coupon_codes", params)
+  end
+
+  def delete(coupon_id) do
+    post_resource(coupon_id, "/delete", %{})
+  end
+
+  def delete_unused_coupon_codes(coupon_id) do
+    post_resource(coupon_id, "/delete_unused_coupon_codes", %{})
+  end
+end
diff --git a/lib/chargebee_elixir/customer.ex b/lib/chargebee_elixir/customer.ex
index 7bf7548..53d15a2 100644
--- a/lib/chargebee_elixir/customer.ex
+++ b/lib/chargebee_elixir/customer.ex
@@ -1,3 +1,10 @@
 defmodule ChargebeeElixir.Customer do
+  @moduledoc """
+  an interface for interacting with Customers
+  """
   use ChargebeeElixir.Resource, "customer"
+
+  def merge(args) do
+    create(args, "/merge")
+  end
 end
diff --git a/lib/chargebee_elixir/event.ex b/lib/chargebee_elixir/event.ex
new file mode 100644
index 0000000..18169bd
--- /dev/null
+++ b/lib/chargebee_elixir/event.ex
@@ -0,0 +1,33 @@
+defmodule ChargebeeElixir.Event do
+  @moduledoc """
+  an interface for interacting with Events
+  """
+  @resource "event"
+  alias ChargebeeElixir.Interface
+
+  def retrieve(id) do
+    id |> resource_path() |> Interface.get() |> Map.get(@resource)
+  rescue
+    ChargebeeElixir.NotFoundError -> nil
+  end
+
+  def list(params \\ %{}) do
+    # Should pagination be by default?
+    case Interface.get(resource_base_path(), params) do
+      %{"list" => current_list, "next_offset" => next_offset} ->
+        Enum.map(current_list, &Map.get(&1, @resource)) ++
+          __MODULE__.list(Map.merge(params, %{"offset" => next_offset}))
+
+      %{"list" => current_list} ->
+        Enum.map(current_list, &Map.get(&1, @resource))
+    end
+  end
+
+  defp resource_base_path do
+    "/#{@resource}s"
+  end
+
+  defp resource_path(id) do
+    "#{resource_base_path()}/#{id}"
+  end
+end
diff --git a/lib/chargebee_elixir/gift.ex b/lib/chargebee_elixir/gift.ex
new file mode 100644
index 0000000..6e41d3d
--- /dev/null
+++ b/lib/chargebee_elixir/gift.ex
@@ -0,0 +1,18 @@
+defmodule ChargebeeElixir.Gift do
+  @moduledoc """
+  An interface for interacting with Chargebee Gifts
+  """
+  use ChargebeeElixir.Resource, "gift"
+
+  def create_for_items(params) do
+    create(params, "/create_for_items")
+  end
+
+  def cancel(coupon_id) do
+    post_resource(coupon_id, "/cancel", %{})
+  end
+
+  def claim(coupon_id) do
+    post_resource(coupon_id, "/claim", %{})
+  end
+end
diff --git a/lib/chargebee_elixir/hosted_page.ex b/lib/chargebee_elixir/hosted_page.ex
index cd3d937..e988291 100644
--- a/lib/chargebee_elixir/hosted_page.ex
+++ b/lib/chargebee_elixir/hosted_page.ex
@@ -1,6 +1,14 @@
 defmodule ChargebeeElixir.HostedPage do
+  @moduledoc """
+  an interface for interacting with HostedPages
+  """
   use ChargebeeElixir.Resource, "hosted_page"
 
-  def checkout_new(params) do create(params, "/checkout_new") end
-  def checkout_existing(params) do create(params, "/checkout_existing") end
+  def checkout_new(params) do
+    create(params, "/checkout_new")
+  end
+
+  def checkout_existing(params) do
+    create(params, "/checkout_existing")
+  end
 end
diff --git a/lib/chargebee_elixir/interface.ex b/lib/chargebee_elixir/interface.ex
index 6715fe6..82ef5be 100644
--- a/lib/chargebee_elixir/interface.ex
+++ b/lib/chargebee_elixir/interface.ex
@@ -1,42 +1,53 @@
 defmodule ChargebeeElixir.Interface do
+  @moduledoc """
+  A low level http interface for interacting with Chargebee V2 HTTP Endpoints
+
+  Configuration:
+   - Authorization loaded from Application env `:chargebee_elixir, :api_key`
+   - Chargebee namespace scoping loaded from  Application env  `:chargebee_elixir, :namespace`
+   - Alternative HTTP Clients configured from  Application env `:chargebee_elixir, :http_client` (i.e. in testing)
+  """
 
   def get(path) do
     get(path, %{})
   end
 
   def get(path, params) do
-    params_string = params
-      |> URI.encode_query()
+    params_string = URI.encode_query(params)
 
-    url = [fullpath(path), params_string]
-      |> Enum.filter(fn(s) -> String.length(s) > 0 end)
+    url =
+      [fullpath(path), params_string]
+      |> Enum.filter(fn s -> String.length(s) > 0 end)
       |> Enum.join("?")
 
-    http_client().get!(url,headers())
-      |> handle_response()
+    http_client().get!(url, headers())
+    |> handle_response()
   end
 
   def post(path, data) do
-    body = data
-      |> transform_arrays_for_chargebee
-      |> Plug.Conn.Query.encode()
+    body =
+      data
+      |> serialize()
+      |> URI.encode_query()
+
     http_client().post!(
       fullpath(path),
       body,
       headers() ++ [{"Content-Type", "application/x-www-form-urlencoded"}]
     )
-      |> handle_response()
+    |> handle_response()
   end
 
   defp handle_response(%{body: body, status_code: 200}) do
-    body
-      |> Jason.decode!
+    Jason.decode!(body)
   end
 
   defp handle_response(%{body: body, status_code: 400}) do
-    message = body
-      |> Jason.decode!
+    message =
+      body
+      |> Jason.decode!()
       |> Map.get("message")
+
     raise ChargebeeElixir.InvalidRequestError, message: message
   end
 
@@ -52,54 +63,79 @@ defmodule ChargebeeElixir.Interface do
     raise ChargebeeElixir.UnknownError
   end
 
-  defp http_client() do
+  defp http_client do
     Application.get_env(:chargebee_elixir, :http_client, HTTPoison)
   end
 
   defp fullpath(path) do
+    # TODO someday: Allow multiple Chargebee Interfaces with multiple namespaces
     namespace = Application.get_env(:chargebee_elixir, :namespace)
     "https://#{namespace}.chargebee.com/api/v2#{path}"
   end
 
-  defp headers() do
-    api_key = Application.get_env(:chargebee_elixir, :api_key)
+  defp headers do
+    api_key =
+      :chargebee_elixir
+      |> Application.get_env(:api_key)
+      |> Kernel.<>(":")
+      |> Base.encode64()
+
     [
-      {"Authorization", "Basic #{"#{api_key}:" |> Base.encode64}"}
+      {"Authorization", "Basic " <> api_key}
     ]
   end
 
-  def transform_arrays_for_chargebee(data) do
-    case data do
-      map_data when is_map(map_data) ->
-        map_data
-          |> Enum.map(fn {k, v} ->
-              {k, transform_arrays_for_chargebee(v)}
-            end)
-          |> Enum.into(%{})
-      list_data when is_list(list_data) ->
-        transformed_list_data = list_data
-          |> Enum.map(fn item -> transform_arrays_for_chargebee(item) end)
-        transformed_list_data
-          |> Enum.map(fn (item) -> case item do
-                map_item when is_map(map_item) -> Map.keys(map_item)
-                _ -> raise ChargebeeElixir.IncorrectDataFormatError,
-                  message: "Unsupported data: lists should contains objects only"
-              end
-            end)
-          |> List.flatten
-          |> Enum.uniq
-          |> Enum.map(fn (key) ->
-            {
-              key,
-              transformed_list_data
-                |> Enum.with_index
-                |> Enum.map(fn {item, index} -> {index, item[key]} end)
-                |> Enum.filter(fn {_index, item} -> !is_nil(item) end)
-                |> Enum.into(%{})
-            }
-          end)
-          |> Enum.into(%{})
-      other_data -> other_data
-    end
+  # serialize/3 is a 1:1 adaptation of Chargebee-Ruby `Chargebee::Util.serialize/3`
+  # from https://github.com/chargebee/chargebee-ruby/blob/42f4aa5e58d5760d9f66d3aff02f8389faa6e68f/lib/chargebee/util.rb#L5
+  def serialize(value, prefix \\ nil, index \\ nil)
+
+  def serialize(value, prefix, index) when is_map(value) do
+    Enum.flat_map(value, fn
+      {_k, nil} ->
+        []
+
+      {k, v} when k in ["metadata", :metadata] and is_map(v) ->
+        [{to_string(k), Jason.encode!(v)}]
+
+      {k, v} when is_map(v) or is_list(v) ->
+        pre = if is_nil(prefix), do: to_string(k), else: "#{prefix}[#{k}]"
+        # fix = if is_nil(index), do: "", else: "[#{index}]"
+
+        serialize(v, pre, index)
+
+      {k, v} ->
+        pre = if is_nil(prefix), do: to_string(k), else: "#{prefix}[#{k}]"
+        fix = if is_nil(index), do: "", else: "[#{index}]"
+
+        key = pre <> fix
+        [{key, to_string(v)}]
+    end)
+    |> Map.new()
+  end
+
+  def serialize(value, prefix, nil) when is_list(value) do
+    value
+    |> Enum.with_index()
+    |> Enum.flat_map(fn {item, i} -> serialize(item, prefix, i) end)
+    |> Map.new()
+  end
+
+  # Apparently Second Degree nested arrays are just encoded as json values
+  def serialize(value, prefix, index) when is_list(value) do
+    value = Jason.encode!(value)
+
+    key = "#{prefix}[#{index}]"
+
+    [{key, value}]
+  end
+
+  def serialize(_value, nil, nil) do
+    raise ArgumentError, "Only hash or arrays are allowed as value"
+  end
+
+  def serialize(value, prefix, index) do
+    key = "#{prefix}[#{index}]"
+
+    [{key, value}]
   end
 end
diff --git a/lib/chargebee_elixir/invoice.ex b/lib/chargebee_elixir/invoice.ex
index 1e49fa9..51e2be7 100644
--- a/lib/chargebee_elixir/invoice.ex
+++ b/lib/chargebee_elixir/invoice.ex
@@ -1,7 +1,14 @@
 defmodule ChargebeeElixir.Invoice do
+  @moduledoc """
+  an interface for interacting with Invoices
+  """
   use ChargebeeElixir.Resource, "invoice"
-  def close(id, params \\ %{}) do post_endpoint(id, "/close", params) end
-  def import_invoice(params \\ %{}) do create(params, "/import_invoice") end
-end
 
-  
+  def import_invoice(params \\ %{}) do 
+    create(params, "/import_invoice") 
+  end
+
+  def close(id, params \\ %{}) do
+    post_resource(id, "/close", params)
+  end
+end
diff --git a/lib/chargebee_elixir/item.ex b/lib/chargebee_elixir/item.ex
new file mode 100644
index 0000000..f7b6cf3
--- /dev/null
+++ b/lib/chargebee_elixir/item.ex
@@ -0,0 +1,6 @@
+defmodule ChargebeeElixir.Item do
+  @moduledoc """
+  an interface for interacting with Items
+  """
+  use ChargebeeElixir.Resource, "item"
+end
diff --git a/lib/chargebee_elixir/item_family.ex b/lib/chargebee_elixir/item_family.ex
new file mode 100644
index 0000000..b8530fd
--- /dev/null
+++ b/lib/chargebee_elixir/item_family.ex
@@ -0,0 +1,6 @@
+defmodule ChargebeeElixir.ItemFamily do
+  @moduledoc """
+  an interface for interacting with Items
+  """
+  use ChargebeeElixir.Resource, "item_family"
+end
diff --git a/lib/chargebee_elixir/item_price.ex b/lib/chargebee_elixir/item_price.ex
new file mode 100644
index 0000000..9255f97
--- /dev/null
+++ b/lib/chargebee_elixir/item_price.ex
@@ -0,0 +1,6 @@
+defmodule ChargebeeElixir.ItemPrice do
+  @moduledoc """
+  an interface for interacting with Items
+  """
+  use ChargebeeElixir.Resource, "item_price"
+end
diff --git a/lib/chargebee_elixir/payment_intent.ex b/lib/chargebee_elixir/payment_intent.ex
new file mode 100644
index 0000000..1f5a8b1
--- /dev/null
+++ b/lib/chargebee_elixir/payment_intent.ex
@@ -0,0 +1,6 @@
+defmodule ChargebeeElixir.PaymentIntent do
+  @moduledoc """
+  an interface for interacting with PaymentIntents
+  """
+  use ChargebeeElixir.Resource, "payment_intent"
+end
diff --git a/lib/chargebee_elixir/payment_source.ex b/lib/chargebee_elixir/payment_source.ex
new file mode 100644
index 0000000..d884735
--- /dev/null
+++ b/lib/chargebee_elixir/payment_source.ex
@@ -0,0 +1,6 @@
+defmodule ChargebeeElixir.PaymentSource do
+  @moduledoc """
+  an interface for interacting with PaymentSources
+  """
+  use ChargebeeElixir.Resource, "payment_source"
+end
diff --git a/lib/chargebee_elixir/plan.ex b/lib/chargebee_elixir/plan.ex
index 79feb34..62b2f8a 100644
--- a/lib/chargebee_elixir/plan.ex
+++ b/lib/chargebee_elixir/plan.ex
@@ -1,3 +1,6 @@
 defmodule ChargebeeElixir.Plan do
+  @moduledoc """
+  an interface for interacting with Plans
+  """
   use ChargebeeElixir.Resource, "plan"
 end
diff --git a/lib/chargebee_elixir/portal_session.ex b/lib/chargebee_elixir/portal_session.ex
index ab467e2..b9c1b98 100644
--- a/lib/chargebee_elixir/portal_session.ex
+++ b/lib/chargebee_elixir/portal_session.ex
@@ -1,3 +1,6 @@
 defmodule ChargebeeElixir.PortalSession do
+  @moduledoc """
+  an interface for interacting with PortalSessions
+  """
   use ChargebeeElixir.Resource, "portal_session"
 end
diff --git a/lib/chargebee_elixir/resource.ex b/lib/chargebee_elixir/resource.ex
index 37a1837..04cad28 100644
--- a/lib/chargebee_elixir/resource.ex
+++ b/lib/chargebee_elixir/resource.ex
@@ -1,50 +1,69 @@
 defmodule ChargebeeElixir.Resource do
+  @moduledoc false
   defmacro __using__(resource) do
-    quote do
+    quote location: :keep do
       alias ChargebeeElixir.Interface
 
       @resource unquote(resource)
+      @resource_plural Inflex.pluralize(@resource)
 
       def retrieve(id) do
-        Interface.get(resource_path(id))[@resource]
+        id |> resource_path() |> Interface.get() |> Map.get(@resource)
       rescue
-        e in ChargebeeElixir.NotFoundError -> nil
+        ChargebeeElixir.NotFoundError -> nil
       end
 
-      def list do
-        __MODULE__.list(%{})
-      end
-
-      def list(params) do
+      def list(params \\ %{}) do
+        # Should pagination be by default?
         case Interface.get(resource_base_path(), params) do
           %{"list" => current_list, "next_offset" => next_offset} ->
-            Enum.map(current_list, fn(hash) -> hash[@resource] end) ++ __MODULE__.list(Map.merge(params, %{"offset" => next_offset}))
+            Enum.map(current_list, &Map.get(&1, @resource)) ++
+              __MODULE__.list(Map.merge(params, %{"offset" => next_offset}))
+
           %{"list" => current_list} ->
-            Enum.map(current_list, fn(hash) -> hash[@resource] end)
+            Enum.map(current_list, &Map.get(&1, @resource))
         end
       end
 
       def create(params, path \\ "") do
-        Interface.post("#{resource_base_path()}#{path}", params)[@resource]
+        resource_base_path()
+        |> Kernel.<>(path)
+        |> Interface.post(params)
+        |> Map.get(@resource)
       end
 
-      def post_endpoint(id, endpoint, params) do
-        Interface.post("#{resource_path(id)}#{endpoint}", params)[@resource]
+      def post_resource(resource_id, endpoint, params) do
+        resource_id
+        |> resource_path()
+        |> Kernel.<>(endpoint)
+        |> Interface.post(params)
+        |> Map.get(@resource)
       end
 
       def create_for_parent(parent_path, params, path \\ "") do
-        Interface.post(
-          "#{parent_path}#{resource_base_path()}#{path}",
-          params
-        )[@resource]
+        parent_path
+        |> Kernel.<>(resource_base_path())
+        |> Kernel.<>(path)
+        |> Interface.post(params)
+        |> Map.get(@resource)
       end
 
-      def resource_base_path() do
-        "/#{@resource}s"
+      def update(resource_id, params, path \\ "") do
+        resource_id
+        |> resource_path()
+        |> Kernel.<>(path)
+        |> Interface.post(params)
+        |> Map.get(@resource)
+      end
+
+      def resource_base_path do
+        "/#{@resource_plural}"
       end
 
       def resource_path(id) do
-        "#{resource_base_path()}/#{id}"
+        encoded_id = id |> to_string |> URI.encode()
+
+        "#{resource_base_path()}/#{encoded_id}"
       end
     end
   end
diff --git a/lib/chargebee_elixir/subscription.ex b/lib/chargebee_elixir/subscription.ex
index ae3407d..54ed281 100644
--- a/lib/chargebee_elixir/subscription.ex
+++ b/lib/chargebee_elixir/subscription.ex
@@ -1,10 +1,12 @@
 defmodule ChargebeeElixir.Subscription do
+  @moduledoc """
+  an interface for interacting with Subscriptions
+  """
   use ChargebeeElixir.Resource, "subscription"
 
   def create_for_customer(customer_id, params) do
-    create_for_parent(
-      ChargebeeElixir.Customer.resource_path(customer_id),
-      params
-    )
+    customer_id
+    |> ChargebeeElixir.Customer.resource_path()
+    |> create_for_parent(params)
   end
 end
diff --git a/mix.exs b/mix.exs
index 44fd3b6..e9c763e 100644
--- a/mix.exs
+++ b/mix.exs
@@ -14,7 +14,7 @@ defmodule ChargebeeElixir.MixProject do
       },
       source_url: "https://github.com/NicolasMarlier/chargebee-elixir",
       homepage_url: "https://github.com/NicolasMarlier/chargebee-elixir",
-      version: "0.1.4",
+      version: "0.2.0",
       elixir: "~> 1.11",
       start_permanent: Mix.env() == :prod,
       deps: deps()
@@ -31,11 +31,14 @@ defmodule ChargebeeElixir.MixProject do
   # Run "mix help deps" to learn about dependencies.
   defp deps do
     [
+      {:inflex, "~> 2.0"},
       {:jason, "~> 1.0"},
       {:httpoison, "~> 1.7"},
-      {:plug, "~>1.11"},
       {:ex_doc, "~> 0.23", only: :dev, runtime: false},
-      {:mox, "~>1.0", only: [:test]}
+      {:mox, "~>1.0", only: [:test]},
+      {:credo, "~> 1.6", only: [:dev, :test], runtime: false},
+      {:dialyxir, ">= 0.0.0", only: [:dev], runtime: false},
+      {:ex_check, "~> 0.14.0", only: [:dev], runtime: false}
     ]
   end
 end
diff --git a/mix.lock b/mix.lock
index 5a778c1..6de337a 100644
--- a/mix.lock
+++ b/mix.lock
@@ -1,22 +1,26 @@
 %{
-  "certifi": {:hex, :certifi, "2.5.2", "b7cfeae9d2ed395695dd8201c57a2d019c0c43ecaf8b8bcb9320b40d6662f340", [:rebar3], [{:parse_trans, "~>3.3", [hex: :parse_trans, repo: "hexpm", optional: false]}], "hexpm", "3b3b5f36493004ac3455966991eaf6e768ce9884693d9968055aeeeb1e575040"},
-  "earmark_parser": {:hex, :earmark_parser, "1.4.12", "b245e875ec0a311a342320da0551da407d9d2b65d98f7a9597ae078615af3449", [:mix], [], "hexpm", "711e2cc4d64abb7d566d43f54b78f7dc129308a63bc103fbd88550d2174b3160"},
-  "ex_doc": {:hex, :ex_doc, "0.23.0", "a069bc9b0bf8efe323ecde8c0d62afc13d308b1fa3d228b65bca5cf8703a529d", [:mix], [{:earmark_parser, "~> 1.4.0", [hex: :earmark_parser, repo: "hexpm", optional: false]}, {:makeup_elixir, "~> 0.14", [hex: :makeup_elixir, repo: "hexpm", optional: false]}], "hexpm", "f5e2c4702468b2fd11b10d39416ddadd2fcdd173ba2a0285ebd92c39827a5a16"},
-  "hackney": {:hex, :hackney, "1.16.0", "5096ac8e823e3a441477b2d187e30dd3fff1a82991a806b2003845ce72ce2d84", [:rebar3], [{:certifi, "2.5.2", [hex: :certifi, repo: "hexpm", optional: false]}, {:idna, "6.0.1", [hex: :idna, repo: "hexpm", optional: false]}, {:metrics, "1.0.1", [hex: :metrics, repo: "hexpm", optional: false]}, {:mimerl, "~>1.1", [hex: :mimerl, repo: "hexpm", optional: false]}, {:parse_trans, "3.3.0", [hex: :parse_trans, repo: "hexpm", optional: false]}, {:ssl_verify_fun, "1.1.6", [hex: :ssl_verify_fun, repo: "hexpm", optional: false]}], "hexpm", "3bf0bebbd5d3092a3543b783bf065165fa5d3ad4b899b836810e513064134e18"},
-  "httpoison": {:hex, :httpoison, "1.7.0", "abba7d086233c2d8574726227b6c2c4f6e53c4deae7fe5f6de531162ce9929a0", [:mix], [{:hackney, "~> 1.16", [hex: :hackney, repo: "hexpm", optional: false]}], "hexpm", "975cc87c845a103d3d1ea1ccfd68a2700c211a434d8428b10c323dc95dc5b980"},
-  "idna": {:hex, :idna, "6.0.1", "1d038fb2e7668ce41fbf681d2c45902e52b3cb9e9c77b55334353b222c2ee50c", [:rebar3], [{:unicode_util_compat, "0.5.0", [hex: :unicode_util_compat, repo: "hexpm", optional: false]}], "hexpm", "a02c8a1c4fd601215bb0b0324c8a6986749f807ce35f25449ec9e69758708122"},
-  "jason": {:hex, :jason, "1.2.2", "ba43e3f2709fd1aa1dce90aaabfd039d000469c05c56f0b8e31978e03fa39052", [:mix], [{:decimal, "~> 1.0 or ~> 2.0", [hex: :decimal, repo: "hexpm", optional: true]}], "hexpm", "18a228f5f0058ee183f29f9eae0805c6e59d61c3b006760668d8d18ff0d12179"},
-  "makeup": {:hex, :makeup, "1.0.5", "d5a830bc42c9800ce07dd97fa94669dfb93d3bf5fcf6ea7a0c67b2e0e4a7f26c", [:mix], [{:nimble_parsec, "~> 0.5 or ~> 1.0", [hex: :nimble_parsec, repo: "hexpm", optional: false]}], "hexpm", "cfa158c02d3f5c0c665d0af11512fed3fba0144cf1aadee0f2ce17747fba2ca9"},
-  "makeup_elixir": {:hex, :makeup_elixir, "0.15.0", "98312c9f0d3730fde4049985a1105da5155bfe5c11e47bdc7406d88e01e4219b", [:mix], [{:makeup, "~> 1.0", [hex: :makeup, repo: "hexpm", optional: false]}, {:nimble_parsec, "~> 1.1", [hex: :nimble_parsec, repo: "hexpm", optional: false]}], "hexpm", "75ffa34ab1056b7e24844c90bfc62aaf6f3a37a15faa76b07bc5eba27e4a8b4a"},
+  "bunt": {:hex, :bunt, "0.2.0", "951c6e801e8b1d2cbe58ebbd3e616a869061ddadcc4863d0a2182541acae9a38", [:mix], [], "hexpm", "7af5c7e09fe1d40f76c8e4f9dd2be7cebd83909f31fee7cd0e9eadc567da8353"},
+  "certifi": {:hex, :certifi, "2.9.0", "6f2a475689dd47f19fb74334859d460a2dc4e3252a3324bd2111b8f0429e7e21", [:rebar3], [], "hexpm", "266da46bdb06d6c6d35fde799bcb28d36d985d424ad7c08b5bb48f5b5cdd4641"},
+  "credo": {:hex, :credo, "1.6.4", "ddd474afb6e8c240313f3a7b0d025cc3213f0d171879429bf8535d7021d9ad78", [:mix], [{:bunt, "~> 0.2.0", [hex: :bunt, repo: "hexpm", optional: false]}, {:file_system, "~> 0.2.8", [hex: :file_system, repo: "hexpm", optional: false]}, {:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: false]}], "hexpm", "c28f910b61e1ff829bffa056ef7293a8db50e87f2c57a9b5c3f57eee124536b7"},
+  "dialyxir": {:hex, :dialyxir, "1.1.0", "c5aab0d6e71e5522e77beff7ba9e08f8e02bad90dfbeffae60eaf0cb47e29488", [:mix], [{:erlex, ">= 0.2.6", [hex: :erlex, repo: "hexpm", optional: false]}], "hexpm", "07ea8e49c45f15264ebe6d5b93799d4dd56a44036cf42d0ad9c960bc266c0b9a"},
+  "earmark_parser": {:hex, :earmark_parser, "1.4.25", "2024618731c55ebfcc5439d756852ec4e85978a39d0d58593763924d9a15916f", [:mix], [], "hexpm", "56749c5e1c59447f7b7a23ddb235e4b3defe276afc220a6227237f3efe83f51e"},
+  "erlex": {:hex, :erlex, "0.2.6", "c7987d15e899c7a2f34f5420d2a2ea0d659682c06ac607572df55a43753aa12e", [:mix], [], "hexpm", "2ed2e25711feb44d52b17d2780eabf998452f6efda104877a3881c2f8c0c0c75"},
+  "ex_check": {:hex, :ex_check, "0.14.0", "d6fbe0bcc51cf38fea276f5bc2af0c9ae0a2bb059f602f8de88709421dae4f0e", [:mix], [], "hexpm", "8a602e98c66e6a4be3a639321f1f545292042f290f91fa942a285888c6868af0"},
+  "ex_doc": {:hex, :ex_doc, "0.28.3", "6eea2f69995f5fba94cd6dd398df369fe4e777a47cd887714a0976930615c9e6", [:mix], [{:earmark_parser, "~> 1.4.19", [hex: :earmark_parser, repo: "hexpm", optional: false]}, {:makeup_elixir, "~> 0.14", [hex: :makeup_elixir, repo: "hexpm", optional: false]}, {:makeup_erlang, "~> 0.1", [hex: :makeup_erlang, repo: "hexpm", optional: false]}], "hexpm", "05387a6a2655b5f9820f3f627450ed20b4325c25977b2ee69bed90af6688e718"},
+  "file_system": {:hex, :file_system, "0.2.10", "fb082005a9cd1711c05b5248710f8826b02d7d1784e7c3451f9c1231d4fc162d", [:mix], [], "hexpm", "41195edbfb562a593726eda3b3e8b103a309b733ad25f3d642ba49696bf715dc"},
+  "hackney": {:hex, :hackney, "1.18.1", "f48bf88f521f2a229fc7bae88cf4f85adc9cd9bcf23b5dc8eb6a1788c662c4f6", [:rebar3], [{:certifi, "~>2.9.0", [hex: :certifi, repo: "hexpm", optional: false]}, {:idna, "~>6.1.0", [hex: :idna, repo: "hexpm", optional: false]}, {:metrics, "~>1.0.0", [hex: :metrics, repo: "hexpm", optional: false]}, {:mimerl, "~>1.1", [hex: :mimerl, repo: "hexpm", optional: false]}, {:parse_trans, "3.3.1", [hex: :parse_trans, repo: "hexpm", optional: false]}, {:ssl_verify_fun, "~>1.1.0", [hex: :ssl_verify_fun, repo: "hexpm", optional: false]}, {:unicode_util_compat, "~>0.7.0", [hex: :unicode_util_compat, repo: "hexpm", optional: false]}], "hexpm", "a4ecdaff44297e9b5894ae499e9a070ea1888c84afdd1fd9b7b2bc384950128e"},
+  "httpoison": {:hex, :httpoison, "1.8.0", "6b85dea15820b7804ef607ff78406ab449dd78bed923a49c7160e1886e987a3d", [:mix], [{:hackney, "~> 1.17", [hex: :hackney, repo: "hexpm", optional: false]}], "hexpm", "28089eaa98cf90c66265b6b5ad87c59a3729bea2e74e9d08f9b51eb9729b3c3a"},
+  "idna": {:hex, :idna, "6.1.1", "8a63070e9f7d0c62eb9d9fcb360a7de382448200fbbd1b106cc96d3d8099df8d", [:rebar3], [{:unicode_util_compat, "~>0.7.0", [hex: :unicode_util_compat, repo: "hexpm", optional: false]}], "hexpm", "92376eb7894412ed19ac475e4a86f7b413c1b9fbb5bd16dccd57934157944cea"},
+  "inflex": {:hex, :inflex, "2.1.0", "a365cf0821a9dacb65067abd95008ca1b0bb7dcdd85ae59965deef2aa062924c", [:mix], [], "hexpm", "14c17d05db4ee9b6d319b0bff1bdf22aa389a25398d1952c7a0b5f3d93162dd8"},
+  "jason": {:hex, :jason, "1.3.0", "fa6b82a934feb176263ad2df0dbd91bf633d4a46ebfdffea0c8ae82953714946", [:mix], [{:decimal, "~> 1.0 or ~> 2.0", [hex: :decimal, repo: "hexpm", optional: true]}], "hexpm", "53fc1f51255390e0ec7e50f9cb41e751c260d065dcba2bf0d08dc51a4002c2ac"},
+  "makeup": {:hex, :makeup, "1.1.0", "6b67c8bc2882a6b6a445859952a602afc1a41c2e08379ca057c0f525366fc3ca", [:mix], [{:nimble_parsec, "~> 1.2.2 or ~> 1.3", [hex: :nimble_parsec, repo: "hexpm", optional: false]}], "hexpm", "0a45ed501f4a8897f580eabf99a2e5234ea3e75a4373c8a52824f6e873be57a6"},
+  "makeup_elixir": {:hex, :makeup_elixir, "0.16.0", "f8c570a0d33f8039513fbccaf7108c5d750f47d8defd44088371191b76492b0b", [:mix], [{:makeup, "~> 1.0", [hex: :makeup, repo: "hexpm", optional: false]}, {:nimble_parsec, "~> 1.2.3", [hex: :nimble_parsec, repo: "hexpm", optional: false]}], "hexpm", "28b2cbdc13960a46ae9a8858c4bebdec3c9a6d7b4b9e7f4ed1502f8159f338e7"},
+  "makeup_erlang": {:hex, :makeup_erlang, "0.1.1", "3fcb7f09eb9d98dc4d208f49cc955a34218fc41ff6b84df7c75b3e6e533cc65f", [:mix], [{:makeup, "~> 1.0", [hex: :makeup, repo: "hexpm", optional: false]}], "hexpm", "174d0809e98a4ef0b3309256cbf97101c6ec01c4ab0b23e926a9e17df2077cbb"},
   "metrics": {:hex, :metrics, "1.0.1", "25f094dea2cda98213cecc3aeff09e940299d950904393b2a29d191c346a8486", [:rebar3], [], "hexpm", "69b09adddc4f74a40716ae54d140f93beb0fb8978d8636eaded0c31b6f099f16"},
-  "mime": {:hex, :mime, "1.5.0", "203ef35ef3389aae6d361918bf3f952fa17a09e8e43b5aa592b93eba05d0fb8d", [:mix], [], "hexpm", "55a94c0f552249fc1a3dd9cd2d3ab9de9d3c89b559c2bd01121f824834f24746"},
   "mimerl": {:hex, :mimerl, "1.2.0", "67e2d3f571088d5cfd3e550c383094b47159f3eee8ffa08e64106cdf5e981be3", [:rebar3], [], "hexpm", "f278585650aa581986264638ebf698f8bb19df297f66ad91b18910dfc6e19323"},
-  "mox": {:hex, :mox, "1.0.0", "4b3c7005173f47ff30641ba044eb0fe67287743eec9bd9545e37f3002b0a9f8b", [:mix], [], "hexpm", "201b0a20b7abdaaab083e9cf97884950f8a30a1350a1da403b3145e213c6f4df"},
-  "nimble_parsec": {:hex, :nimble_parsec, "1.1.0", "3a6fca1550363552e54c216debb6a9e95bd8d32348938e13de5eda962c0d7f89", [:mix], [], "hexpm", "08eb32d66b706e913ff748f11694b17981c0b04a33ef470e33e11b3d3ac8f54b"},
-  "parse_trans": {:hex, :parse_trans, "3.3.0", "09765507a3c7590a784615cfd421d101aec25098d50b89d7aa1d66646bc571c1", [:rebar3], [], "hexpm", "17ef63abde837ad30680ea7f857dd9e7ced9476cdd7b0394432af4bfc241b960"},
-  "plug": {:hex, :plug, "1.11.0", "f17217525597628298998bc3baed9f8ea1fa3f1160aa9871aee6df47a6e4d38e", [:mix], [{:mime, "~> 1.0", [hex: :mime, repo: "hexpm", optional: false]}, {:plug_crypto, "~> 1.1.1 or ~> 1.2", [hex: :plug_crypto, repo: "hexpm", optional: false]}, {:telemetry, "~> 0.4", [hex: :telemetry, repo: "hexpm", optional: false]}], "hexpm", "2d9c633f0499f9dc5c2fd069161af4e2e7756890b81adcbb2ceaa074e8308876"},
-  "plug_crypto": {:hex, :plug_crypto, "1.2.0", "1cb20793aa63a6c619dd18bb33d7a3aa94818e5fd39ad357051a67f26dfa2df6", [:mix], [], "hexpm", "a48b538ae8bf381ffac344520755f3007cc10bd8e90b240af98ea29b69683fc2"},
+  "mox": {:hex, :mox, "1.0.1", "b651bf0113265cda0ba3a827fcb691f848b683c373b77e7d7439910a8d754d6e", [:mix], [], "hexpm", "35bc0dea5499d18db4ef7fe4360067a59b06c74376eb6ab3bd67e6295b133469"},
+  "nimble_parsec": {:hex, :nimble_parsec, "1.2.3", "244836e6e3f1200c7f30cb56733fd808744eca61fd182f731eac4af635cc6d0b", [:mix], [], "hexpm", "c8d789e39b9131acf7b99291e93dae60ab48ef14a7ee9d58c6964f59efb570b0"},
+  "parse_trans": {:hex, :parse_trans, "3.3.1", "16328ab840cc09919bd10dab29e431da3af9e9e7e7e6f0089dd5a2d2820011d8", [:rebar3], [], "hexpm", "07cd9577885f56362d414e8c4c4e6bdf10d43a8767abb92d24cbe8b24c54888b"},
   "ssl_verify_fun": {:hex, :ssl_verify_fun, "1.1.6", "cf344f5692c82d2cd7554f5ec8fd961548d4fd09e7d22f5b62482e5aeaebd4b0", [:make, :mix, :rebar3], [], "hexpm", "bdb0d2471f453c88ff3908e7686f86f9be327d065cc1ec16fa4540197ea04680"},
-  "telemetry": {:hex, :telemetry, "0.4.2", "2808c992455e08d6177322f14d3bdb6b625fbcfd233a73505870d8738a2f4599", [:rebar3], [], "hexpm", "2d1419bd9dda6a206d7b5852179511722e2b18812310d304620c7bd92a13fcef"},
-  "unicode_util_compat": {:hex, :unicode_util_compat, "0.5.0", "8516502659002cec19e244ebd90d312183064be95025a319a6c7e89f4bccd65b", [:rebar3], [], "hexpm", "d48d002e15f5cc105a696cf2f1bbb3fc72b4b770a184d8420c8db20da2674b38"},
+  "unicode_util_compat": {:hex, :unicode_util_compat, "0.7.0", "bc84380c9ab48177092f43ac89e4dfa2c6d62b40b8bd132b1059ecc7232f9a78", [:rebar3], [], "hexpm", "25eee6d67df61960cf6a794239566599b09e17e668d3700247bc498638152521"},
 }
diff --git a/test/chargebee_elixir/addon_test.exs b/test/chargebee_elixir/addon_test.exs
index 95d0955..a5aceb6 100644
--- a/test/chargebee_elixir/addon_test.exs
+++ b/test/chargebee_elixir/addon_test.exs
@@ -9,9 +9,10 @@ defmodule ChargebeeElixir.AddonTest do
       expect(
         ChargebeeElixir.HTTPoisonMock,
         :get!,
-        fn (url, headers) ->
+        fn url, headers ->
           assert url == "https://test-namespace.chargebee.com/api/v2/addons/1234"
           assert headers == [{"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"}]
+
           %{
             status_code: 401
           }
@@ -27,9 +28,10 @@ defmodule ChargebeeElixir.AddonTest do
       expect(
         ChargebeeElixir.HTTPoisonMock,
         :get!,
-        fn (url, headers) ->
+        fn url, headers ->
           assert url == "https://test-namespace.chargebee.com/api/v2/addons/1234"
           assert headers == [{"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"}]
+
           %{
             status_code: 404
           }
@@ -43,9 +45,10 @@ defmodule ChargebeeElixir.AddonTest do
       expect(
         ChargebeeElixir.HTTPoisonMock,
         :get!,
-        fn (url, headers) ->
+        fn url, headers ->
           assert url == "https://test-namespace.chargebee.com/api/v2/addons/1234"
           assert headers == [{"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"}]
+
           %{
             status_code: 200,
             body: '{"addon": {"id": 1234}}'
@@ -62,9 +65,10 @@ defmodule ChargebeeElixir.AddonTest do
       expect(
         ChargebeeElixir.HTTPoisonMock,
         :get!,
-        fn (url, headers) ->
+        fn url, headers ->
           assert url == "https://test-namespace.chargebee.com/api/v2/addons"
           assert headers == [{"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"}]
+
           %{
             status_code: 401
           }
@@ -80,9 +84,10 @@ defmodule ChargebeeElixir.AddonTest do
       expect(
         ChargebeeElixir.HTTPoisonMock,
         :get!,
-        fn (url, headers) ->
+        fn url, headers ->
           assert url == "https://test-namespace.chargebee.com/api/v2/addons"
           assert headers == [{"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"}]
+
           %{
             status_code: 200,
             body: '{"list": [{"addon": {"id": 1234}}]}'
@@ -97,9 +102,12 @@ defmodule ChargebeeElixir.AddonTest do
       expect(
         ChargebeeElixir.HTTPoisonMock,
         :get!,
-        fn (url, headers) ->
-          assert url == "https://test-namespace.chargebee.com/api/v2/addons?id%5Bin%5D=%5B1234%2C1235%5D"
+        fn url, headers ->
+          assert url ==
+                   "https://test-namespace.chargebee.com/api/v2/addons?id%5Bin%5D=%5B1234%2C1235%5D"
+
           assert headers == [{"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"}]
+
           %{
             status_code: 200,
             body: '{
@@ -113,9 +121,12 @@ defmodule ChargebeeElixir.AddonTest do
       expect(
         ChargebeeElixir.HTTPoisonMock,
         :get!,
-        fn (url, headers) ->
-          assert url == "https://test-namespace.chargebee.com/api/v2/addons?id%5Bin%5D=%5B1234%2C1235%5D&offset=1235"
+        fn url, headers ->
+          assert url ==
+                   "https://test-namespace.chargebee.com/api/v2/addons?id%5Bin%5D=%5B1234%2C1235%5D&offset=1235"
+
           assert headers == [{"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"}]
+
           %{
             status_code: 200,
             body: '{
@@ -125,7 +136,10 @@ defmodule ChargebeeElixir.AddonTest do
         end
       )
 
-      assert ChargebeeElixir.Addon.list(%{"id[in]": "[1234,1235]"}) == [%{"id" => 1234}, %{"id" => 1235}]
+      assert ChargebeeElixir.Addon.list(%{"id[in]": "[1234,1235]"}) == [
+               %{"id" => 1234},
+               %{"id" => 1235}
+             ]
     end
   end
 
@@ -134,13 +148,15 @@ defmodule ChargebeeElixir.AddonTest do
       expect(
         ChargebeeElixir.HTTPoisonMock,
         :post!,
-        fn (url, data, headers) ->
+        fn url, data, headers ->
           assert url == "https://test-namespace.chargebee.com/api/v2/addons"
           assert data == "id=addon-a"
+
           assert headers == [
-            {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
-            {"Content-Type", "application/x-www-form-urlencoded"}
-          ]
+                   {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
+                   {"Content-Type", "application/x-www-form-urlencoded"}
+                 ]
+
           %{
             status_code: 401
           }
@@ -156,13 +172,15 @@ defmodule ChargebeeElixir.AddonTest do
       expect(
         ChargebeeElixir.HTTPoisonMock,
         :post!,
-        fn (url, data, headers) ->
+        fn url, data, headers ->
           assert url == "https://test-namespace.chargebee.com/api/v2/addons"
           assert data == "id=addon-a"
+
           assert headers == [
-            {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
-            {"Content-Type", "application/x-www-form-urlencoded"}
-          ]
+                   {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
+                   {"Content-Type", "application/x-www-form-urlencoded"}
+                 ]
+
           %{
             status_code: 400,
             body: '{"message": "Unknown"}'
@@ -179,13 +197,15 @@ defmodule ChargebeeElixir.AddonTest do
       expect(
         ChargebeeElixir.HTTPoisonMock,
         :post!,
-        fn (url, data, headers) ->
+        fn url, data, headers ->
           assert url == "https://test-namespace.chargebee.com/api/v2/addons"
           assert data == "id=addon-a"
+
           assert headers == [
-            {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
-            {"Content-Type", "application/x-www-form-urlencoded"}
-          ]
+                   {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
+                   {"Content-Type", "application/x-www-form-urlencoded"}
+                 ]
+
           %{
             status_code: 200,
             body: '{"addon": {"id": "addon-a"}}'
diff --git a/test/chargebee_elixir/coupon_test.exs b/test/chargebee_elixir/coupon_test.exs
new file mode 100644
index 0000000..c466cbc
--- /dev/null
+++ b/test/chargebee_elixir/coupon_test.exs
@@ -0,0 +1,77 @@
+defmodule ChargebeeElixir.CouponTest do
+  use ExUnit.Case
+  doctest ChargebeeElixir.Coupon
+  alias ChargebeeElixir.Coupon
+  import Mox
+
+  setup :verify_on_exit!
+
+  def subject do
+  end
+
+  describe "create_for_items" do
+    test "works with exmaple data from chargebee" do
+      expect(
+        ChargebeeElixir.HTTPoisonMock,
+        :post!,
+        fn url, data, _headers ->
+          assert url ==
+                   "https://test-namespace.chargebee.com/api/v2/coupons/create_for_items"
+
+          assert URI.decode(data) ==
+                   "apply_on=each_specified_item&discount_percentage=10.0&discount_type=percentage&duration_type=forever&id=summer_offer&item_constraints[constraint][0]=all&item_constraints[item_type][0]=plan&name=Summer+Offer"
+
+          %{
+            status_code: 200,
+            body: '{"coupon": {"id": "summer_offer"}}'
+          }
+        end
+      )
+
+      assert Coupon.create_for_items(%{
+               id: "summer_offer",
+               name: "Summer Offer",
+               discount_percentage: 10.0,
+               discount_type: "percentage",
+               duration_type: "forever",
+               apply_on: "each_specified_item",
+               item_constraints: [%{constraint: "all", item_type: "plan"}]
+             }) == %{"id" => "summer_offer"}
+    end
+
+    test "works with list of  item_price_ids" do
+      expect(
+        ChargebeeElixir.HTTPoisonMock,
+        :post!,
+        fn url, data, _headers ->
+          assert url ==
+                   "https://test-namespace.chargebee.com/api/v2/coupons/create_for_items"
+
+          assert URI.decode(data) ==
+                   "apply_on=each_specified_item&discount_percentage=10.0&discount_type=percentage&duration_type=forever&id=summer_offer&item_constraints[constraint][0]=specific&item_constraints[item_price_ids][0]=[\"item_1\"]&item_constraints[item_type][0]=plan&name=Summer+Offer"
+
+          %{
+            status_code: 200,
+            body: '{"coupon": {"id": "summer_offer"}}'
+          }
+        end
+      )
+
+      assert Coupon.create_for_items(%{
+               id: "summer_offer",
+               name: "Summer Offer",
+               discount_percentage: 10.0,
+               discount_type: "percentage",
+               duration_type: "forever",
+               apply_on: "each_specified_item",
+               item_constraints: [
+                 %{
+                   constraint: "specific",
+                   item_type: "plan",
+                   item_price_ids: ["item_1"]
+                 }
+               ]
+             }) == %{"id" => "summer_offer"}
+    end
+  end
+end
diff --git a/test/chargebee_elixir/hosted_page_test.exs b/test/chargebee_elixir/hosted_page_test.exs
index 440278b..eb79ca3 100644
--- a/test/chargebee_elixir/hosted_page_test.exs
+++ b/test/chargebee_elixir/hosted_page_test.exs
@@ -9,13 +9,17 @@ defmodule ChargebeeElixir.HostedPageTest do
       expect(
         ChargebeeElixir.HTTPoisonMock,
         :post!,
-        fn (url, data, headers) ->
+        fn url, data, headers ->
           assert url == "https://test-namespace.chargebee.com/api/v2/hosted_pages/checkout_new"
-          assert data == "addons[id][0]=addon-a&addons[id][1]=addon-b&subscription[plan_id]=plan-a"
+
+          assert URI.decode(data) ==
+                   "addons[id][0]=addon-a&addons[id][1]=addon-b&subscription[plan_id]=plan-a"
+
           assert headers == [
-            {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
-            {"Content-Type", "application/x-www-form-urlencoded"}
-          ]
+                   {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
+                   {"Content-Type", "application/x-www-form-urlencoded"}
+                 ]
+
           %{
             status_code: 200,
             body: '{"hosted_page": {"url": "https://doe.com"}}'
@@ -24,14 +28,14 @@ defmodule ChargebeeElixir.HostedPageTest do
       )
 
       assert ChargebeeElixir.HostedPage.checkout_new(%{
-        subscription: %{
-          plan_id: "plan-a",
-        },
-        addons: [
-          %{ id: "addon-a"},
-          %{ id: "addon-b"}
-        ]
-        }) == %{"url" => "https://doe.com"}
+               subscription: %{
+                 plan_id: "plan-a"
+               },
+               addons: [
+                 %{id: "addon-a"},
+                 %{id: "addon-b"}
+               ]
+             }) == %{"url" => "https://doe.com"}
     end
   end
 
@@ -40,13 +44,18 @@ defmodule ChargebeeElixir.HostedPageTest do
       expect(
         ChargebeeElixir.HTTPoisonMock,
         :post!,
-        fn (url, data, headers) ->
-          assert url == "https://test-namespace.chargebee.com/api/v2/hosted_pages/checkout_existing"
-          assert data == "addons[id][0]=addon-a&addons[id][1]=addon-b&customer[id]=cus-a&subscription[id]=subscription-a&subscription[plan_id]=plan-a"
+        fn url, data, headers ->
+          assert url ==
+                   "https://test-namespace.chargebee.com/api/v2/hosted_pages/checkout_existing"
+
+          assert URI.decode(data) ==
+                   "addons[id][0]=addon-a&addons[id][1]=addon-b&customer[id]=cus-a&subscription[id]=subscription-a&subscription[plan_id]=plan-a"
+
           assert headers == [
-            {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
-            {"Content-Type", "application/x-www-form-urlencoded"}
-          ]
+                   {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
+                   {"Content-Type", "application/x-www-form-urlencoded"}
+                 ]
+
           %{
             status_code: 200,
             body: '{"hosted_page": {"url": "https://doe.com"}}'
@@ -55,18 +64,18 @@ defmodule ChargebeeElixir.HostedPageTest do
       )
 
       assert ChargebeeElixir.HostedPage.checkout_existing(%{
-        subscription: %{
-          id: "subscription-a",
-          plan_id: "plan-a",
-        },
-        customer: %{
-          id: "cus-a"
-        },
-        addons: [
-          %{ id: "addon-a"},
-          %{ id: "addon-b"}
-        ]
-        }) == %{"url" => "https://doe.com"}
+               subscription: %{
+                 id: "subscription-a",
+                 plan_id: "plan-a"
+               },
+               customer: %{
+                 id: "cus-a"
+               },
+               addons: [
+                 %{id: "addon-a"},
+                 %{id: "addon-b"}
+               ]
+             }) == %{"url" => "https://doe.com"}
     end
   end
 end
diff --git a/test/chargebee_elixir/interface_test.exs b/test/chargebee_elixir/interface_test.exs
index 30c755a..f7b246e 100644
--- a/test/chargebee_elixir/interface_test.exs
+++ b/test/chargebee_elixir/interface_test.exs
@@ -1,130 +1,183 @@
 defmodule ChargebeeElixir.InterfaceTest do
   use ExUnit.Case
 
-  describe "transform_arrays_for_chargebee" do
-    test "simple list" do
-      assert ChargebeeElixir.Interface.transform_arrays_for_chargebee([
-        %{id: "object-a"},
-        %{id: "object-b"}
-      ]) == %{
-        id: %{
-          0 => "object-a",
-          1 => "object-b"
+  describe "serialize" do
+    test "chargebee example" do
+      # from chargebee-ruby test case
+      input = %{
+        :id => "sub_KyVq7DNSNM7CSD",
+        :plan_id => "free",
+        :addons => [%{:id => "monitor", :quantity => 2}, %{:id => "ssl"}],
+        :addon_ids => ["addon_one", "addon_two"],
+        :card => %{
+          :first_name => "Rajaraman",
+          :last_name => "Santhanam",
+          :number => "4111111111111111",
+          :expiry_month => "1",
+          :expiry_year => "2024",
+          :cvv => "007"
         }
       }
-    end
 
-    test "deep nesting, no lists" do
-      assert ChargebeeElixir.Interface.transform_arrays_for_chargebee(%{
-        addon: %{
-          id: "addon-a",
-          nested: %{
-            object: %{
-              id: "object-a"
-            }
-          }
-        }
-      }) == %{
-        addon: %{
-          id: "addon-a",
-          nested: %{
-            object: %{
-              id: "object-a"
-            }
-          }
-        }
+      output = %{
+        "id" => "sub_KyVq7DNSNM7CSD",
+        "plan_id" => "free",
+        "addons[id][0]" => "monitor",
+        "addons[quantity][0]" => "2",
+        "addons[id][1]" => "ssl",
+        "addon_ids[0]" => "addon_one",
+        "addon_ids[1]" => "addon_two",
+        "card[first_name]" => "Rajaraman",
+        "card[last_name]" => "Santhanam",
+        "card[number]" => "4111111111111111",
+        "card[expiry_month]" => "1",
+        "card[expiry_year]" => "2024",
+        "card[cvv]" => "007"
       }
+
+      assert ChargebeeElixir.Interface.serialize(input) == output
     end
 
-    test "simple nesting" do
-      assert ChargebeeElixir.Interface.transform_arrays_for_chargebee(%{
+    test "chargebeee example 2" do
+      # From the chargebee-go Test case
+      input = %{
+        plan_id: "cbdemo_grow",
+        customer: %{
+          email: "john@user.com",
+          first_name: "John",
+          last_name: "Doe",
+          locale: "frCA",
+          phone: "+19499999999",
+          auto_collection: "on"
+        },
         addons: [
           %{
-            id: "addon-a",
-            price: 10
+            id: "cbdemo_conciergesupport"
           },
           %{
-            id: "addon-b",
+            id: "cbdemo_additionaluser",
             quantity: 2
           }
-        ]
-      }) == %{
-        addons: %{
-          id: %{
-            0 => "addon-a",
-            1 => "addon-b"
-          },
-          price: %{
-            0 => 10
-          },
-          quantity: %{
-            1 => 2
-          }
-        }
+        ],
+        coupon_ids: ["cbdemo_earlybird"]
+      }
+
+      output = %{
+        "coupon_ids[0]" => "cbdemo_earlybird",
+        "customer[phone]" => "+19499999999",
+        "plan_id" => "cbdemo_grow",
+        "customer[last_name]" => "Doe",
+        "customer[locale]" => "frCA",
+        "addons[id][0]" => "cbdemo_conciergesupport",
+        "addons[id][1]" => "cbdemo_additionaluser",
+        "addons[quantity][1]" => "2",
+        "customer[email]" => "john@user.com",
+        "customer[auto_collection]" => "on",
+        "customer[first_name]" => "John"
       }
+
+      assert ChargebeeElixir.Interface.serialize(input) == output
+    end
+
+    test "simple list" do
+      assert ChargebeeElixir.Interface.serialize([
+               %{id: "object-a"},
+               %{id: "object-b"}
+             ]) == %{"id[0]" => "object-a", "id[1]" => "object-b"}
     end
 
-    test "incorrect nesting" do
-      assert_raise ChargebeeElixir.IncorrectDataFormatError,
-        "Unsupported data: lists should contains objects only", fn ->
-        ChargebeeElixir.Interface.transform_arrays_for_chargebee(%{
-          addons: [
-            %{
-              id: "addon-a",
-              price: 10
-            },
-            %{
-              id: "addon-b",
-              quantity: 2
-            },
-            "a"
-          ]
-        })
-      end
+    test "deep nesting, no lists" do
+      assert ChargebeeElixir.Interface.serialize(%{
+               addon: %{
+                 id: "addon-a",
+                 nested: %{
+                   object: %{
+                     id: "object-a"
+                   }
+                 }
+               }
+             }) == %{"addon[id]" => "addon-a", "addon[nested][object][id]" => "object-a"}
     end
 
-    test "complex nesting" do
-      assert ChargebeeElixir.Interface.transform_arrays_for_chargebee(%{
-        addons: [
-          %{
-            id: "addon-a",
-            price: 10,
-            nested_objects: [
-              %{
-                id: "object-a"
-              },
-              %{
-                id: "object-b"
-              }
-            ]
-          },
+    test "simple nesting" do
+      assert ChargebeeElixir.Interface.serialize(%{
+               addons: [
+                 %{
+                   id: "addon-a",
+                   price: 10
+                 },
+                 %{
+                   id: "addon-b",
+                   quantity: 2
+                 }
+               ]
+             }) == %{
+               "addons[id][0]" => "addon-a",
+               "addons[id][1]" => "addon-b",
+               "addons[price][0]" => "10",
+               "addons[quantity][1]" => "2"
+             }
+    end
+
+    test "Example of complex nested list field" do
+      assert ChargebeeElixir.Interface.serialize(%{
+               item_constraints: [
+                 %{
+                   constraint: "specific",
+                   item_type: "plan",
+                   item_price_ids: ["item_a"]
+                 }
+               ]
+             }) == %{
+               "item_constraints[constraint][0]" => "specific",
+               "item_constraints[item_type][0]" => "plan",
+               "item_constraints[item_price_ids][0]" => "[\"item_a\"]"
+             }
+    end
+
+    test "when query encoded" do
+      input = %{
+        item_constraints: [
           %{
-            id: "addon-b",
-            quantity: 2
+            constraint: "specific",
+            item_type: "plan",
+            item_price_ids: "[\"item_a\"]"
           }
         ]
-      }) == %{
-        addons: %{
-          id: %{
-            0 => "addon-a",
-            1 => "addon-b"
-          },
-          price: %{
-            0 => 10
-          },
-          quantity: %{
-            1 => 2
-          },
-          nested_objects: %{
-            0 => %{
-              id: %{
-                0 => "object-a",
-                1 => "object-b"
-              }
-            }
-          }
-        }
       }
+
+      as_encoded_params =
+        ~s<item_constraints[constraint][0]=specific&item_constraints[item_price_ids][0]=["item_a"]&item_constraints[item_type][0]=plan>
+
+      assert as_encoded_params ==
+               input
+               |> ChargebeeElixir.Interface.serialize()
+               |> URI.encode_query()
+               |> URI.decode()
+    end
+
+    test "drops nil fields" do
+      # from chargebee-ruby test case
+      input = %{
+        :id => "sub_KyVq7DNSNM7CSD",
+        :plan_id => "free",
+        :item_family_id => nil
+      }
+
+      output = %{
+        "id" => "sub_KyVq7DNSNM7CSD",
+        "plan_id" => "free"
+      }
+
+      assert ChargebeeElixir.Interface.serialize(input) == output
+    end
+
+    test "serializes metadata as encoded json" do
+      input = %{metadata: %{some: "value"}}
+
+      output = %{"metadata" => ~S({"some":"value"})}
+
+      assert ChargebeeElixir.Interface.serialize(input) == output
     end
   end
 end
diff --git a/test/chargebee_elixir/invoice_test.exs b/test/chargebee_elixir/invoice_test.exs
index ba02ece..d468e6f 100644
--- a/test/chargebee_elixir/invoice_test.exs
+++ b/test/chargebee_elixir/invoice_test.exs
@@ -20,13 +20,17 @@ defmodule ChargebeeElixir.InvoiceTest do
       expect(
         ChargebeeElixir.HTTPoisonMock,
         :post!,
-        fn (url, data, headers) ->
-          assert url == "https://test-namespace.chargebee.com/api/v2/invoices/draft_inv_abcde/close"
+        fn url, data, headers ->
+          assert url ==
+                   "https://test-namespace.chargebee.com/api/v2/invoices/draft_inv_abcde/close"
+
           assert data == "invoice_note=This+is+a+note"
+
           assert headers == [
-            {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
-            {"Content-Type", "application/x-www-form-urlencoded"}
-          ]
+                   {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
+                   {"Content-Type", "application/x-www-form-urlencoded"}
+                 ]
+
           %{
             status_code: 401
           }
@@ -42,13 +46,17 @@ defmodule ChargebeeElixir.InvoiceTest do
       expect(
         ChargebeeElixir.HTTPoisonMock,
         :post!,
-        fn (url, data, headers) ->
-          assert url == "https://test-namespace.chargebee.com/api/v2/invoices/draft_inv_abcde/close"
+        fn url, data, headers ->
+          assert url ==
+                   "https://test-namespace.chargebee.com/api/v2/invoices/draft_inv_abcde/close"
+
           assert data == "invoice_note=This+is+a+note"
+
           assert headers == [
-            {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
-            {"Content-Type", "application/x-www-form-urlencoded"}
-          ]
+                   {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
+                   {"Content-Type", "application/x-www-form-urlencoded"}
+                 ]
+
           %{
             status_code: 404
           }
@@ -64,13 +72,17 @@ defmodule ChargebeeElixir.InvoiceTest do
       expect(
         ChargebeeElixir.HTTPoisonMock,
         :post!,
-        fn (url, data, headers) ->
-          assert url == "https://test-namespace.chargebee.com/api/v2/invoices/draft_inv_abcde/close"
+        fn url, data, headers ->
+          assert url ==
+                   "https://test-namespace.chargebee.com/api/v2/invoices/draft_inv_abcde/close"
+
           assert data == "invoice_note=This+is+a+note"
+
           assert headers == [
-            {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
-            {"Content-Type", "application/x-www-form-urlencoded"}
-          ]
+                   {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
+                   {"Content-Type", "application/x-www-form-urlencoded"}
+                 ]
+
           %{
             status_code: 400,
             body: '{"message": "Unknown"}'
@@ -87,13 +99,17 @@ defmodule ChargebeeElixir.InvoiceTest do
       expect(
         ChargebeeElixir.HTTPoisonMock,
         :post!,
-        fn (url, data, headers) ->
-          assert url == "https://test-namespace.chargebee.com/api/v2/invoices/draft_inv_abcde/close"
+        fn url, data, headers ->
+          assert url ==
+                   "https://test-namespace.chargebee.com/api/v2/invoices/draft_inv_abcde/close"
+
           assert data == "invoice_note=This+is+a+note"
+
           assert headers == [
-            {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
-            {"Content-Type", "application/x-www-form-urlencoded"}
-          ]
+                   {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
+                   {"Content-Type", "application/x-www-form-urlencoded"}
+                 ]
+
           %{
             status_code: 200,
             body: '{"invoice": {"id": "abcde"}}'
diff --git a/test/chargebee_elixir/portal_session_test.exs b/test/chargebee_elixir/portal_session_test.exs
index 6cb08e7..4e31944 100644
--- a/test/chargebee_elixir/portal_session_test.exs
+++ b/test/chargebee_elixir/portal_session_test.exs
@@ -9,13 +9,15 @@ defmodule ChargebeeElixir.PortalSessionTest do
       expect(
         ChargebeeElixir.HTTPoisonMock,
         :post!,
-        fn (url, data, headers) ->
+        fn url, data, headers ->
           assert url == "https://test-namespace.chargebee.com/api/v2/portal_sessions"
           assert data == ""
+
           assert headers == [
-            {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
-            {"Content-Type", "application/x-www-form-urlencoded"}
-          ]
+                   {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
+                   {"Content-Type", "application/x-www-form-urlencoded"}
+                 ]
+
           %{
             status_code: 401
           }
@@ -31,13 +33,15 @@ defmodule ChargebeeElixir.PortalSessionTest do
       expect(
         ChargebeeElixir.HTTPoisonMock,
         :post!,
-        fn (url, data, headers) ->
+        fn url, data, headers ->
           assert url == "https://test-namespace.chargebee.com/api/v2/portal_sessions"
           assert data == ""
+
           assert headers == [
-            {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
-            {"Content-Type", "application/x-www-form-urlencoded"}
-          ]
+                   {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
+                   {"Content-Type", "application/x-www-form-urlencoded"}
+                 ]
+
           %{
             status_code: 400,
             body: '{"message": "Unknown"}'
@@ -54,13 +58,17 @@ defmodule ChargebeeElixir.PortalSessionTest do
       expect(
         ChargebeeElixir.HTTPoisonMock,
         :post!,
-        fn (url, data, headers) ->
+        fn url, data, headers ->
           assert url == "https://test-namespace.chargebee.com/api/v2/portal_sessions"
-          assert data == "customer[id]=cus_1234&redirect_url=https%3A%2F%2Fredirect.com"
+
+          assert URI.decode(data) ==
+                   "customer[id]=cus_1234&redirect_url=https://redirect.com"
+
           assert headers == [
-            {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
-            {"Content-Type", "application/x-www-form-urlencoded"}
-          ]
+                   {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
+                   {"Content-Type", "application/x-www-form-urlencoded"}
+                 ]
+
           %{
             status_code: 200,
             body: '{"portal_session": {"url": "https://doe.com"}}'
@@ -69,11 +77,11 @@ defmodule ChargebeeElixir.PortalSessionTest do
       )
 
       assert ChargebeeElixir.PortalSession.create(%{
-        redirect_url: "https://redirect.com",
-        customer: %{
-          id: "cus_1234"
-        }
-        }) == %{"url" => "https://doe.com"}
+               redirect_url: "https://redirect.com",
+               customer: %{
+                 id: "cus_1234"
+               }
+             }) == %{"url" => "https://doe.com"}
     end
   end
 end
diff --git a/test/chargebee_elixir/subscription_test.exs b/test/chargebee_elixir/subscription_test.exs
index 170ec50..0b96c90 100644
--- a/test/chargebee_elixir/subscription_test.exs
+++ b/test/chargebee_elixir/subscription_test.exs
@@ -11,7 +11,7 @@ defmodule ChargebeeElixir.SubscriptionTest do
         plan_id: "plan-a",
         addons: [
           %{id: "addon-a"},
-          %{id: "addon-b"},
+          %{id: "addon-b"}
         ]
       }
     )
@@ -22,13 +22,17 @@ defmodule ChargebeeElixir.SubscriptionTest do
       expect(
         ChargebeeElixir.HTTPoisonMock,
         :post!,
-        fn (url, data, headers) ->
-          assert url == "https://test-namespace.chargebee.com/api/v2/customers/cus_1/subscriptions"
-          assert data == "addons[id][0]=addon-a&addons[id][1]=addon-b&plan_id=plan-a"
+        fn url, data, headers ->
+          assert url ==
+                   "https://test-namespace.chargebee.com/api/v2/customers/cus_1/subscriptions"
+
+          assert URI.decode(data) == "addons[id][0]=addon-a&addons[id][1]=addon-b&plan_id=plan-a"
+
           assert headers == [
-            {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
-            {"Content-Type", "application/x-www-form-urlencoded"}
-          ]
+                   {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
+                   {"Content-Type", "application/x-www-form-urlencoded"}
+                 ]
+
           %{
             status_code: 401
           }
@@ -44,13 +48,17 @@ defmodule ChargebeeElixir.SubscriptionTest do
       expect(
         ChargebeeElixir.HTTPoisonMock,
         :post!,
-        fn (url, data, headers) ->
-          assert url == "https://test-namespace.chargebee.com/api/v2/customers/cus_1/subscriptions"
-          assert data == "addons[id][0]=addon-a&addons[id][1]=addon-b&plan_id=plan-a"
+        fn url, data, headers ->
+          assert url ==
+                   "https://test-namespace.chargebee.com/api/v2/customers/cus_1/subscriptions"
+
+          assert URI.decode(data) == "addons[id][0]=addon-a&addons[id][1]=addon-b&plan_id=plan-a"
+
           assert headers == [
-            {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
-            {"Content-Type", "application/x-www-form-urlencoded"}
-          ]
+                   {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
+                   {"Content-Type", "application/x-www-form-urlencoded"}
+                 ]
+
           %{
             status_code: 404
           }
@@ -66,13 +74,17 @@ defmodule ChargebeeElixir.SubscriptionTest do
       expect(
         ChargebeeElixir.HTTPoisonMock,
         :post!,
-        fn (url, data, headers) ->
-          assert url == "https://test-namespace.chargebee.com/api/v2/customers/cus_1/subscriptions"
-          assert data == "addons[id][0]=addon-a&addons[id][1]=addon-b&plan_id=plan-a"
+        fn url, data, headers ->
+          assert url ==
+                   "https://test-namespace.chargebee.com/api/v2/customers/cus_1/subscriptions"
+
+          assert URI.decode(data) == "addons[id][0]=addon-a&addons[id][1]=addon-b&plan_id=plan-a"
+
           assert headers == [
-            {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
-            {"Content-Type", "application/x-www-form-urlencoded"}
-          ]
+                   {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
+                   {"Content-Type", "application/x-www-form-urlencoded"}
+                 ]
+
           %{
             status_code: 400,
             body: '{"message": "Unknown"}'
@@ -89,13 +101,17 @@ defmodule ChargebeeElixir.SubscriptionTest do
       expect(
         ChargebeeElixir.HTTPoisonMock,
         :post!,
-        fn (url, data, headers) ->
-          assert url == "https://test-namespace.chargebee.com/api/v2/customers/cus_1/subscriptions"
-          assert data == "addons[id][0]=addon-a&addons[id][1]=addon-b&plan_id=plan-a"
+        fn url, data, headers ->
+          assert url ==
+                   "https://test-namespace.chargebee.com/api/v2/customers/cus_1/subscriptions"
+
+          assert URI.decode(data) == "addons[id][0]=addon-a&addons[id][1]=addon-b&plan_id=plan-a"
+
           assert headers == [
-            {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
-            {"Content-Type", "application/x-www-form-urlencoded"}
-          ]
+                   {"Authorization", "Basic dGVzdF9jaGFyZ2VlYmVlX2FwaV9rZXk6"},
+                   {"Content-Type", "application/x-www-form-urlencoded"}
+                 ]
+
           %{
             status_code: 200,
             body: '{"subscription": {"id": "sub-a"}}'