Error 204 when sending API request to the Back-End, said to be caused by CORS Credential. Previous independent testing made by calling the back-end directly from the browser and found that the endpoint shouldn't be using '/api', but no help even after changing the front-end's routing to the back-end with or without '/api', still the same Error 204. So, the front-end's routing ended up reverted back to using '/api' as original.

What had been done afterward (following the suggestion from the AI Agent): changing the front-end API component to allow credential (withCredentials: true)

Result: the same Error 204 and some axios error