fix: handle tip service API errors safely

src/services/__tests__/tipService.test.ts

@@ -50,6 +50,17 @@ describe('tipService', () => {
     );
   });
 
+  it('uses the fallback message when the API error payload is not a string', async () => {
+    mockFetch.mockResolvedValueOnce({
+      ok: false,
+      json: async () => ({ error: { detail: 'Bad request' } }),
+    });
+
+    await expect(sendTip({ recipientId: 'user-99', amount: 0.05 })).rejects.toThrow(
+      'Unable to send tip.',
+    );
+  });
+
   it('throws when the API returns an error', async () => {
     mockFetch.mockResolvedValueOnce({
       ok: false,

src/services/tipService.ts

@@ -25,11 +25,18 @@ export async function sendTip(payload: TipPayload): Promise<TipSendResult> {
   });
 
   if (!response.ok) {
-    const responseBody = (await response.json().catch(() => null)) as {
-      error?: string;
-      message?: string;
+    const errorBody = (await response.json().catch(() => null)) as {
+      error?: unknown;
+      message?: unknown;
     } | null;
-    const message = responseBody?.error ?? responseBody?.message ?? 'Unable to send tip.';
+
+    const message =
+      typeof errorBody?.error === 'string'
+        ? errorBody.error
+        : typeof errorBody?.message === 'string'
+          ? errorBody.message
+          : 'Unable to send tip.';
+
     throw new Error(message);
   }