diff --git a/mpt_api_client/http/async_client.py b/mpt_api_client/http/async_client.py
index 7ce90539..1de2f23d 100644
--- a/mpt_api_client/http/async_client.py
+++ b/mpt_api_client/http/async_client.py
@@ -1,24 +1,23 @@
 import os
-from typing import Any, override
+from typing import Any
 
-from httpx import URL, AsyncClient, AsyncHTTPTransport, HTTPError, HTTPStatusError, Response
-from httpx._client import USE_CLIENT_DEFAULT, UseClientDefault  # noqa: PLC2701
-from httpx._types import (  # noqa: WPS235
-    AuthTypes,
-    CookieTypes,
-    HeaderTypes,
-    QueryParamTypes,
-    RequestContent,
-    RequestData,
-    RequestExtensions,
-    RequestFiles,
-    TimeoutTypes,
+from httpx import (
+    AsyncClient,
+    AsyncHTTPTransport,
+    HTTPError,
+    HTTPStatusError,
 )
 
 from mpt_api_client.exceptions import MPTError, transform_http_status_exception
+from mpt_api_client.http.types import (
+    HeaderTypes,
+    QueryParam,
+    RequestFiles,
+    Response,
+)
 
 
-class AsyncHTTPClient(AsyncClient):
+class AsyncHTTPClient:
     """Async HTTP client for interacting with SoftwareOne Marketplace Platform API."""
 
     def __init__(
@@ -49,43 +48,49 @@ def __init__(
             "Authorization": f"Bearer {api_token}",
             "Accept": "application/json",
         }
-        super().__init__(
+        self.httpx_client = AsyncClient(
             base_url=base_url,
             headers=base_headers,
             timeout=timeout,
             transport=AsyncHTTPTransport(retries=retries),
         )
 
-    @override
     async def request(  # noqa: WPS211
         self,
         method: str,
-        url: URL | str,
+        url: str,
         *,
-        content: RequestContent | None = None,  # noqa: WPS110
-        data: RequestData | None = None,  # noqa: WPS110
         files: RequestFiles | None = None,
         json: Any | None = None,
-        params: QueryParamTypes | None = None,  # noqa: WPS110
+        query_params: QueryParam | None = None,
         headers: HeaderTypes | None = None,
-        cookies: CookieTypes | None = None,
-        auth: AuthTypes | UseClientDefault | None = USE_CLIENT_DEFAULT,
-        follow_redirects: bool | UseClientDefault = USE_CLIENT_DEFAULT,
-        timeout: TimeoutTypes | UseClientDefault = USE_CLIENT_DEFAULT,
-        extensions: RequestExtensions | None = None,
     ) -> Response:
+        """Perform an HTTP request.
+
+        Args:
+            method: HTTP method.
+            url: URL to send the request to.
+            files: Request files.
+            json: Request JSON data.
+            query_params: Query parameters.
+            headers: Request headers.
+
+        Returns:
+            Response object.
+
+        Raises:
+            MPTError: If the request fails.
+            MPTApiError: If the response contains an error.
+            MPTHttpError: If the response contains an HTTP error.
+        """
         try:
-            response = await super().request(
+            response = await self.httpx_client.request(
                 method,
                 url,
-                content=content,
-                data=data,
                 files=files,
                 json=json,
-                params=params,
+                params=query_params,
                 headers=headers,
-                cookies=cookies,
-                auth=auth,
             )
         except HTTPError as err:
             raise MPTError(f"HTTP Error: {err}") from err
@@ -94,4 +99,8 @@ async def request(  # noqa: WPS211
             response.raise_for_status()
         except HTTPStatusError as http_status_exception:
             raise transform_http_status_exception(http_status_exception) from http_status_exception
-        return response
+        return Response(
+            headers=dict(response.headers),
+            status_code=response.status_code,
+            content=response.content,
+        )
diff --git a/mpt_api_client/http/async_service.py b/mpt_api_client/http/async_service.py
index 7b07a484..1e19df8b 100644
--- a/mpt_api_client/http/async_service.py
+++ b/mpt_api_client/http/async_service.py
@@ -1,11 +1,9 @@
 from collections.abc import AsyncIterator
 from urllib.parse import urljoin
 
-import httpx
-
 from mpt_api_client.http.async_client import AsyncHTTPClient
 from mpt_api_client.http.base_service import ServiceBase
-from mpt_api_client.http.types import QueryParam
+from mpt_api_client.http.types import QueryParam, Response
 from mpt_api_client.models import Collection, ResourceData
 from mpt_api_client.models import Model as BaseModel
 from mpt_api_client.models.collection import ResourceList
@@ -77,17 +75,17 @@ async def iterate(self, batch_size: int = 100) -> AsyncIterator[Model]:
                 break
             offset = items_collection.meta.pagination.next_offset()
 
-    async def _fetch_page_as_response(self, limit: int = 100, offset: int = 0) -> httpx.Response:
+    async def _fetch_page_as_response(self, limit: int = 100, offset: int = 0) -> Response:
         """Fetch one page of resources.
 
         Returns:
-            httpx.Response object.
+            Response object.
 
         Raises:
             HTTPStatusError: if the response status code is not 200.
         """
         pagination_params: dict[str, int] = {"limit": limit, "offset": offset}
-        return await self.http_client.get(self.build_url(pagination_params))
+        return await self.http_client.request("get", self.build_url(pagination_params))
 
     async def _resource_do_request(  # noqa: WPS211
         self,
@@ -97,7 +95,7 @@ async def _resource_do_request(  # noqa: WPS211
         json: ResourceData | ResourceList | None = None,
         query_params: QueryParam | None = None,
         headers: dict[str, str] | None = None,
-    ) -> httpx.Response:
+    ) -> Response:
         """Perform an action on a specific resource using.
 
         Request with action: `HTTP_METHOD /endpoint/{resource_id}/{action}`.
@@ -117,7 +115,7 @@ async def _resource_do_request(  # noqa: WPS211
         resource_url = urljoin(f"{self.endpoint}/", resource_id)
         url = urljoin(f"{resource_url}/", action) if action else resource_url
         return await self.http_client.request(
-            method, url, json=json, params=query_params, headers=headers
+            method, url, json=json, query_params=query_params, headers=headers
         )
 
     async def _resource_action(
diff --git a/mpt_api_client/http/base_service.py b/mpt_api_client/http/base_service.py
index c8ee2a07..d37558ea 100644
--- a/mpt_api_client/http/base_service.py
+++ b/mpt_api_client/http/base_service.py
@@ -1,8 +1,7 @@
 import copy
 from typing import Any, Self
 
-import httpx
-
+from mpt_api_client.http.types import Response
 from mpt_api_client.models import Collection, Meta
 from mpt_api_client.models import Model as BaseModel
 from mpt_api_client.rql import RQLQuery
@@ -122,7 +121,7 @@ def select(self, *fields: str) -> Self:
         return new_client
 
     @classmethod
-    def _create_collection(cls, response: httpx.Response) -> Collection[Model]:
+    def _create_collection(cls, response: Response) -> Collection[Model]:
         meta = Meta.from_response(response)
         return Collection(
             resources=[
diff --git a/mpt_api_client/http/client.py b/mpt_api_client/http/client.py
index 61921898..915298d8 100644
--- a/mpt_api_client/http/client.py
+++ b/mpt_api_client/http/client.py
@@ -1,35 +1,26 @@
 import os
-from typing import Any, override
+from typing import Any
 
 from httpx import (
-    URL,
-    USE_CLIENT_DEFAULT,
     Client,
     HTTPError,
     HTTPStatusError,
     HTTPTransport,
-    Response,
-)
-from httpx._client import UseClientDefault
-from httpx._types import (
-    AuthTypes,
-    CookieTypes,
-    HeaderTypes,
-    QueryParamTypes,
-    RequestContent,
-    RequestData,
-    RequestExtensions,
-    TimeoutTypes,
 )
-from respx.types import RequestFiles
 
 from mpt_api_client.exceptions import (
     MPTError,
     transform_http_status_exception,
 )
+from mpt_api_client.http.types import (
+    HeaderTypes,
+    QueryParam,
+    RequestFiles,
+    Response,
+)
 
 
-class HTTPClient(Client):
+class HTTPClient:
     """Sync HTTP client for interacting with SoftwareOne Marketplace Platform API."""
 
     def __init__(
@@ -60,43 +51,49 @@ def __init__(
             "Authorization": f"Bearer {api_token}",
             "content-type": "application/json",
         }
-        super().__init__(
+        self.httpx_client = Client(
             base_url=base_url,
             headers=base_headers,
             timeout=timeout,
             transport=HTTPTransport(retries=retries),
         )
 
-    @override
     def request(  # noqa: WPS211
         self,
         method: str,
-        url: URL | str,
+        url: str,
         *,
-        content: RequestContent | None = None,  # noqa: WPS110
-        data: RequestData | None = None,  # noqa: WPS110
         files: RequestFiles | None = None,
         json: Any | None = None,
-        params: QueryParamTypes | None = None,  # noqa: WPS110
+        query_params: QueryParam | None = None,
         headers: HeaderTypes | None = None,
-        cookies: CookieTypes | None = None,
-        auth: AuthTypes | UseClientDefault | None = USE_CLIENT_DEFAULT,
-        follow_redirects: bool | UseClientDefault = USE_CLIENT_DEFAULT,
-        timeout: TimeoutTypes | UseClientDefault = USE_CLIENT_DEFAULT,
-        extensions: RequestExtensions | None = None,
     ) -> Response:
+        """Perform an HTTP request.
+
+        Args:
+            method: HTTP method.
+            url: URL to send the request to.
+            files: Request files.
+            json: Request JSON data.
+            query_params: Query parameters.
+            headers: Request headers.
+
+        Returns:
+            Response object.
+
+        Raises:
+            MPTError: If the request fails.
+            MPTApiError: If the response contains an error.
+            MPTHttpError: If the response contains an HTTP error.
+        """
         try:
-            response = super().request(
+            response = self.httpx_client.request(
                 method,
                 url,
-                content=content,
-                data=data,
                 files=files,
                 json=json,
-                params=params,
+                params=query_params,
                 headers=headers,
-                cookies=cookies,
-                auth=auth,
             )
         except HTTPError as err:
             raise MPTError(f"HTTP Error: {err}") from err
@@ -105,4 +102,8 @@ def request(  # noqa: WPS211
             response.raise_for_status()
         except HTTPStatusError as http_status_exception:
             raise transform_http_status_exception(http_status_exception) from http_status_exception
-        return response
+        return Response(
+            headers=dict(response.headers),
+            status_code=response.status_code,
+            content=response.content,
+        )
diff --git a/mpt_api_client/http/mixins.py b/mpt_api_client/http/mixins.py
index 24ca296f..04d28ab2 100644
--- a/mpt_api_client/http/mixins.py
+++ b/mpt_api_client/http/mixins.py
@@ -1,9 +1,7 @@
 import json
 from urllib.parse import urljoin
 
-from httpx import Response
-from httpx._types import FileTypes
-
+from mpt_api_client.http.types import FileTypes, Response
 from mpt_api_client.models import FileModel, ResourceData
 
 
@@ -22,7 +20,7 @@ def create(self, resource_data: ResourceData) -> Model:
         Returns:
             New resource created.
         """
-        response = self.http_client.post(self.endpoint, json=resource_data)  # type: ignore[attr-defined]
+        response = self.http_client.request("post", self.endpoint, json=resource_data)  # type: ignore[attr-defined]
 
         return self._model_class.from_response(response)  # type: ignore[attr-defined, no-any-return]
 
@@ -84,7 +82,7 @@ def create(
                 "application/json",
             )
 
-        response = self.http_client.post(self.endpoint, files=files)  # type: ignore[attr-defined]
+        response = self.http_client.request("post", self.endpoint, files=files)  # type: ignore[attr-defined]
 
         return self._model_class.from_response(response)  # type: ignore[attr-defined, no-any-return]
 
@@ -112,7 +110,7 @@ async def create(self, resource_data: ResourceData) -> Model:
         Returns:
             New resource created.
         """
-        response = await self.http_client.post(self.endpoint, json=resource_data)  # type: ignore[attr-defined]
+        response = await self.http_client.request("post", self.endpoint, json=resource_data)  # type: ignore[attr-defined]
 
         return self._model_class.from_response(response)  # type: ignore[attr-defined, no-any-return]
 
@@ -127,7 +125,7 @@ async def delete(self, resource_id: str) -> None:
             resource_id: Resource ID.
         """
         url = urljoin(f"{self.endpoint}/", resource_id)  # type: ignore[attr-defined]
-        await self.http_client.delete(url)  # type: ignore[attr-defined]
+        await self.http_client.request("delete", url)  # type: ignore[attr-defined]
 
 
 class AsyncUpdateMixin[Model]:
@@ -175,7 +173,7 @@ async def create(
                 "application/json",
             )
 
-        response = await self.http_client.post(self.endpoint, files=files)  # type: ignore[attr-defined]
+        response = await self.http_client.request("post", self.endpoint, files=files)  # type: ignore[attr-defined]
 
         return self._model_class.from_response(response)  # type: ignore[attr-defined, no-any-return]
 
diff --git a/mpt_api_client/http/service.py b/mpt_api_client/http/service.py
index 73bf4fe5..33be4827 100644
--- a/mpt_api_client/http/service.py
+++ b/mpt_api_client/http/service.py
@@ -1,11 +1,9 @@
 from collections.abc import Iterator
 from urllib.parse import urljoin
 
-import httpx
-
 from mpt_api_client.http.base_service import ServiceBase
 from mpt_api_client.http.client import HTTPClient
-from mpt_api_client.http.types import QueryParam
+from mpt_api_client.http.types import QueryParam, Response
 from mpt_api_client.models import Collection, ResourceData
 from mpt_api_client.models import Model as BaseModel
 from mpt_api_client.models.collection import ResourceList
@@ -76,17 +74,17 @@ def iterate(self, batch_size: int = 100) -> Iterator[Model]:
                 break
             offset = items_collection.meta.pagination.next_offset()
 
-    def _fetch_page_as_response(self, limit: int = 100, offset: int = 0) -> httpx.Response:
+    def _fetch_page_as_response(self, limit: int = 100, offset: int = 0) -> Response:
         """Fetch one page of resources.
 
         Returns:
-            httpx.Response object.
+            Response object.
 
         Raises:
             HTTPStatusError: if the response status code is not 200.
         """
         pagination_params: dict[str, int] = {"limit": limit, "offset": offset}
-        return self.http_client.get(self.build_url(pagination_params))
+        return self.http_client.request("get", self.build_url(pagination_params))
 
     def _resource_do_request(  # noqa: WPS211
         self,
@@ -96,7 +94,7 @@ def _resource_do_request(  # noqa: WPS211
         json: ResourceData | ResourceList | None = None,
         query_params: QueryParam | None = None,
         headers: dict[str, str] | None = None,
-    ) -> httpx.Response:
+    ) -> Response:
         """Perform an action on a specific resource using `HTTP_METHOD /endpoint/{resource_id}`.
 
         Args:
@@ -116,7 +114,7 @@ def _resource_do_request(  # noqa: WPS211
         resource_url = urljoin(f"{self.endpoint}/", resource_id)
         url = urljoin(f"{resource_url}/", action) if action else resource_url
         return self.http_client.request(
-            method, url, json=json, params=query_params, headers=headers
+            method, url, json=json, query_params=query_params, headers=headers
         )
 
     def _resource_action(
diff --git a/mpt_api_client/http/types.py b/mpt_api_client/http/types.py
index 3a0992ff..11ecef27 100644
--- a/mpt_api_client/http/types.py
+++ b/mpt_api_client/http/types.py
@@ -1,2 +1,42 @@
+import json
+from collections.abc import Mapping, Sequence
+from typing import IO, Any
+
 PrimitiveType = str | int | float | bool | None
 QueryParam = dict[str, PrimitiveType]
+HeaderTypes = dict[str, str]
+
+# Borrowed from HTTPX's "private" types.
+FileContent = IO[bytes] | bytes | str
+FileTypes = (
+    # file (or bytes)
+    FileContent
+    |
+    # (filename, file (or bytes))
+    tuple[str | None, FileContent]
+    |
+    # (filename, file (or bytes), content_type)
+    tuple[str | None, FileContent, str | None]
+    |
+    # (filename, file (or bytes), content_type, headers)
+    tuple[str | None, FileContent, str | None, Mapping[str, str]]  # noqa: WPS221
+)
+RequestFiles = Mapping[str, FileTypes] | Sequence[tuple[str, FileTypes]]  # noqa: WPS221
+
+
+class Response:
+    """HTTP Response."""
+
+    def __init__(self, headers: HeaderTypes, status_code: int, content: bytes):  # noqa: WPS110
+        self.headers = headers
+        self.status_code = status_code
+        self.content = content  # noqa: WPS110
+
+    @property
+    def text(self) -> str:
+        """Content of the response, as text."""
+        return self.content.decode()
+
+    def json(self, **kwargs: Any) -> Any:
+        """Return the json-encoded content of a response, if any."""
+        return json.loads(self.content, **kwargs)
diff --git a/mpt_api_client/models/file_model.py b/mpt_api_client/models/file_model.py
index da29d4de..18636f4c 100644
--- a/mpt_api_client/models/file_model.py
+++ b/mpt_api_client/models/file_model.py
@@ -1,6 +1,6 @@
 import re
 
-from httpx import Response
+from mpt_api_client.http.types import Response
 
 
 class FileModel:
diff --git a/mpt_api_client/models/meta.py b/mpt_api_client/models/meta.py
index e9bb2905..6dd97759 100644
--- a/mpt_api_client/models/meta.py
+++ b/mpt_api_client/models/meta.py
@@ -2,7 +2,7 @@
 from dataclasses import dataclass, field
 from typing import Self
 
-from httpx import Response
+from mpt_api_client.http.types import Response
 
 
 @dataclass
diff --git a/mpt_api_client/models/model.py b/mpt_api_client/models/model.py
index 758809b0..c43da7a2 100644
--- a/mpt_api_client/models/model.py
+++ b/mpt_api_client/models/model.py
@@ -1,8 +1,8 @@
 from typing import Any, ClassVar, Self, override
 
 from box import Box
-from httpx import Response
 
+from mpt_api_client.http.types import Response
 from mpt_api_client.models.meta import Meta
 
 ResourceData = dict[str, Any]
diff --git a/mpt_api_client/resources/notifications/batches.py b/mpt_api_client/resources/notifications/batches.py
index b1e2ae1e..8d053c8f 100644
--- a/mpt_api_client/resources/notifications/batches.py
+++ b/mpt_api_client/resources/notifications/batches.py
@@ -49,7 +49,7 @@ def create(
                 "application/json",
             )
 
-        response = self.http_client.post(self.endpoint, files=files)
+        response = self.http_client.request("post", self.endpoint, files=files)
         return self._model_class.from_response(response)
 
     def get_batch_attachment(self, batch_id: str, attachment_id: str) -> FileModel:
@@ -62,7 +62,9 @@ def get_batch_attachment(self, batch_id: str, attachment_id: str) -> FileModel:
         Returns:
             FileModel containing the attachment.
         """
-        response = self.http_client.get(f"{self.endpoint}/{batch_id}/attachments/{attachment_id}")
+        response = self.http_client.request(
+            "get", f"{self.endpoint}/{batch_id}/attachments/{attachment_id}"
+        )
 
         return FileModel(response)
 
@@ -99,7 +101,7 @@ async def create(
                 "application/json",
             )
 
-        response = await self.http_client.post(self.endpoint, files=files)
+        response = await self.http_client.request("post", self.endpoint, files=files)
         return self._model_class.from_response(response)
 
     async def get_batch_attachment(self, batch_id: str, attachment_id: str) -> FileModel:
@@ -112,7 +114,7 @@ async def get_batch_attachment(self, batch_id: str, attachment_id: str) -> FileM
         Returns:
             FileModel containing the attachment.
         """
-        response = await self.http_client.get(
-            f"{self.endpoint}/{batch_id}/attachments/{attachment_id}"
+        response = await self.http_client.request(
+            "get", f"{self.endpoint}/{batch_id}/attachments/{attachment_id}"
         )
         return FileModel(response)
diff --git a/tests/http/test_async_client.py b/tests/http/test_async_client.py
index dfc3134e..85452d90 100644
--- a/tests/http/test_async_client.py
+++ b/tests/http/test_async_client.py
@@ -1,28 +1,58 @@
+import json
+
 import pytest
 import respx
-from httpx import ConnectTimeout, Response, codes
+from httpx import ConnectTimeout, Request, Response, codes
 
 from mpt_api_client.exceptions import MPTError
 from mpt_api_client.http.async_client import AsyncHTTPClient
 from tests.conftest import API_TOKEN, API_URL
 
 
-def test_async_http_initialization():
-    client = AsyncHTTPClient(base_url=API_URL, api_token=API_TOKEN)
+@pytest.fixture
+def mock_request():
+    return Request("GET", url="/")
 
-    assert client.base_url == API_URL
-    assert client.headers["Authorization"] == "Bearer test-token"
-    assert client.headers["User-Agent"] == "swo-marketplace-client/1.0"
 
+@pytest.fixture
+def mock_response(mock_request):
+    return Response(200, json={"message": "Hello, World!"}, request=mock_request)
 
-def test_async_http_env_initialization(monkeypatch):
-    monkeypatch.setenv("MPT_TOKEN", API_TOKEN)
-    monkeypatch.setenv("MPT_URL", API_URL)
 
-    client = AsyncHTTPClient()
+def test_async_http_initialization(mocker):
+    mock_async_client = mocker.patch("mpt_api_client.http.async_client.AsyncClient")
 
-    assert client.base_url == API_URL
-    assert client.headers["Authorization"] == f"Bearer {API_TOKEN}"
+    AsyncHTTPClient(base_url=API_URL, api_token=API_TOKEN)
+
+    mock_async_client.assert_called_once_with(
+        base_url=API_URL,
+        headers={
+            "User-Agent": "swo-marketplace-client/1.0",
+            "Authorization": "Bearer test-token",
+            "Accept": "application/json",
+        },
+        timeout=5.0,
+        transport=mocker.ANY,
+    )
+
+
+def test_async_env_initialization(monkeypatch, mocker):
+    monkeypatch.setenv("MPT_TOKEN", API_TOKEN)
+    monkeypatch.setenv("MPT_URL", API_URL)
+    mock_async_client = mocker.patch("mpt_api_client.http.async_client.AsyncClient")
+
+    AsyncHTTPClient()
+
+    mock_async_client.assert_called_once_with(
+        base_url=API_URL,
+        headers={
+            "User-Agent": "swo-marketplace-client/1.0",
+            "Authorization": f"Bearer {API_TOKEN}",
+            "Accept": "application/json",
+        },
+        timeout=5.0,
+        transport=mocker.ANY,
+    )
 
 
 def test_async_http_without_token():
@@ -36,15 +66,13 @@ def test_async_http_without_url():
 
 
 @respx.mock
-async def test_async_http_call_success(async_http_client):
-    success_route = respx.get(f"{API_URL}/").mock(
-        return_value=Response(200, json={"message": "Hello, World!"})
-    )
+async def test_async_http_call_success(async_http_client, mock_response):
+    success_route = respx.get(f"{API_URL}/").mock(return_value=mock_response)
 
-    success_response = await async_http_client.get("/")
+    success_response = await async_http_client.request("GET", "/")
 
     assert success_response.status_code == codes.OK
-    assert success_response.json() == {"message": "Hello, World!"}
+    assert json.loads(success_response.content) == {"message": "Hello, World!"}
     assert success_route.called
 
 
@@ -53,6 +81,6 @@ async def test_async_http_call_failure(async_http_client):
     timeout_route = respx.get(f"{API_URL}/timeout").mock(side_effect=ConnectTimeout("Mock Timeout"))
 
     with pytest.raises(MPTError, match="HTTP Error: Mock Timeout"):
-        await async_http_client.get("/timeout")
+        await async_http_client.request("GET", "/timeout")
 
     assert timeout_route.called
diff --git a/tests/http/test_client.py b/tests/http/test_client.py
index b47c663d..313c45e1 100644
--- a/tests/http/test_client.py
+++ b/tests/http/test_client.py
@@ -1,3 +1,5 @@
+import json
+
 import pytest
 import respx
 from httpx import ConnectTimeout, Response, codes
@@ -7,22 +9,40 @@
 from tests.conftest import API_TOKEN, API_URL
 
 
-def test_http_initialization():
-    client = HTTPClient(base_url=API_URL, api_token=API_TOKEN)
+def test_http_initialization(mocker):
+    mock_client = mocker.patch("mpt_api_client.http.client.Client")
+
+    HTTPClient(base_url=API_URL, api_token=API_TOKEN)
 
-    assert client.base_url == API_URL
-    assert client.headers["Authorization"] == "Bearer test-token"
-    assert client.headers["User-Agent"] == "swo-marketplace-client/1.0"
+    mock_client.assert_called_once_with(
+        base_url=API_URL,
+        headers={
+            "User-Agent": "swo-marketplace-client/1.0",
+            "Authorization": "Bearer test-token",
+            "content-type": "application/json",
+        },
+        timeout=5.0,
+        transport=mocker.ANY,
+    )
 
 
-def test_env_initialization(monkeypatch):
+def test_env_initialization(monkeypatch, mocker):
     monkeypatch.setenv("MPT_TOKEN", API_TOKEN)
     monkeypatch.setenv("MPT_URL", API_URL)
-
-    client = HTTPClient()
-
-    assert client.base_url == API_URL
-    assert client.headers["Authorization"] == f"Bearer {API_TOKEN}"
+    mock_client = mocker.patch("mpt_api_client.http.client.Client")
+
+    HTTPClient()
+
+    mock_client.assert_called_once_with(
+        base_url=API_URL,
+        headers={
+            "User-Agent": "swo-marketplace-client/1.0",
+            "Authorization": f"Bearer {API_TOKEN}",
+            "content-type": "application/json",
+        },
+        timeout=5.0,
+        transport=mocker.ANY,
+    )
 
 
 def test_http_without_token():
@@ -41,10 +61,10 @@ def test_http_call_success(http_client):
         return_value=Response(200, json={"message": "Hello, World!"})
     )
 
-    success_response = http_client.get("/")
+    success_response = http_client.request("GET", "/")
 
     assert success_response.status_code == codes.OK
-    assert success_response.json() == {"message": "Hello, World!"}
+    assert json.loads(success_response.content) == {"message": "Hello, World!"}
     assert success_route.called
 
 
@@ -53,6 +73,6 @@ def test_http_call_failure(http_client):
     timeout_route = respx.get(f"{API_URL}/timeout").mock(side_effect=ConnectTimeout("Mock Timeout"))
 
     with pytest.raises(MPTError, match="HTTP Error: Mock Timeout"):
-        http_client.get("/timeout")
+        http_client.request("GET", "/timeout")
 
     assert timeout_route.called
diff --git a/tests/test_exceptions.py b/tests/test_exceptions.py
index db3a7942..10ee6c5f 100644
--- a/tests/test_exceptions.py
+++ b/tests/test_exceptions.py
@@ -52,6 +52,19 @@ def test_api_error_str_and_repr():
     )
 
 
+def test_api_error_str_no_errors():
+    payload = {
+        "status": "400",
+        "title": "Bad Request",
+        "detail": "Invalid input",
+        "traceId": "abc123",
+    }
+
+    exception = MPTAPIError(status_code=400, payload=payload)
+
+    assert str(exception) == "400 Bad Request - Invalid input (abc123)"
+
+
 def test_transform_http_status_exception():
     payload = {
         "status": "400",