diff --git a/.changeset/fix-provider-strict-mode-client.md b/.changeset/fix-provider-strict-mode-client.md
new file mode 100644
index 00000000..3be885a2
--- /dev/null
+++ b/.changeset/fix-provider-strict-mode-client.md
@@ -0,0 +1,15 @@
+---
+"@ledgerhq/wallet-api-client-react": patch
+---
+
+fix(client-react): create WalletAPIClient once in WalletAPIProvider
+
+`WalletAPIProvider` created its client inside a `useState` initializer. Because
+the `WalletAPIClient` constructor has a side effect — it registers itself on
+`transport.onMessage` — React strict mode's double-invocation constructed a
+second, discarded client whose constructor hijacked the transport. Responses
+were then routed to a client with no pending requests, throwing
+`no ongoingRequest`.
+
+The client is now instantiated exactly once via the ref "create once" pattern,
+so a single instance owns the transport even under strict mode.
diff --git a/examples/client-nextjs/app/page.tsx b/examples/client-nextjs/app/page.tsx
index 02993996..8e4e01ac 100644
--- a/examples/client-nextjs/app/page.tsx
+++ b/examples/client-nextjs/app/page.tsx
@@ -11,7 +11,7 @@ import { AccountsList } from "../components/AccountsList";
 const isSimulator =
   typeof window === "undefined"
     ? false
-    : new URLSearchParams(window.location.search).get("simulator");
+    : new URLSearchParams(window.location.search).has("simulator");
 
 function getWalletAPITransport() {
   if (typeof window === "undefined") {
diff --git a/packages/client-react/src/components/WalletAPIProvider/index.tsx b/packages/client-react/src/components/WalletAPIProvider/index.tsx
index bf89a395..ccc15805 100644
--- a/packages/client-react/src/components/WalletAPIProvider/index.tsx
+++ b/packages/client-react/src/components/WalletAPIProvider/index.tsx
@@ -1,5 +1,5 @@
 import { WalletAPIClient } from "@ledgerhq/wallet-api-client";
-import { useEffect, useMemo, useState } from "react";
+import { useEffect, useMemo, useRef, useState } from "react";
 import { WalletAPIProviderContext, initialContextValue } from "./context";
 import type {
   WalletAPIProviderContextState,
@@ -21,11 +21,22 @@ export function WalletAPIProvider({
     initialContextValue.state,
   );
 
-  const [client] = useState<WalletAPIClient | undefined>(
-    () =>
-      providedClient ??
-      new WalletAPIClient(transport, logger, getCustomModule, eventHandlers),
-  );
+  // A WalletAPIClient registers itself on `transport.onMessage` in its
+  // constructor, so it must be instantiated exactly once. A `useState`
+  // initializer is unsafe here: React strict mode invokes it twice, which
+  // constructs a second (discarded) client whose constructor hijacks the
+  // transport, leaving responses routed to a client with no pending requests
+  // ("no ongoingRequest"). The ref "create once" pattern guarantees a single
+  // instance that owns the transport.
+  const clientRef = useRef<WalletAPIClient | undefined>(undefined);
+  clientRef.current ??=
+    providedClient ??
+    new WalletAPIClient(transport, logger, getCustomModule, eventHandlers);
+  // Reading the ref during render is intentional here: the client is created
+  // once (above) and its identity is stable for the lifetime of the provider,
+  // so it can safely be passed down without triggering re-renders.
+  // eslint-disable-next-line react-hooks/refs -- stable create-once instance
+  const client = clientRef.current;
 
   useEffect(() => {
     if (eventHandlers) {