Why is my custom endpoint returning a 404 Not Found error?

A 404 error usually occurs because your permalinks are not flushed. Whenever you register a new route, WordPress needs to rebuild its internal rewrite rules. Simply navigate to Settings > Permalinks in your WordPress dashboard and click "Save Changes" without modifying anything. This action flushes the rewrite cache and registers your custom WordPress API endpoint correctly.

Why am I getting a 401 Unauthorized when testing via Postman?

If your permission_callback requires is_user_logged_in(), testing from an external tool like Postman will fail because Postman does not share your browser's authentication cookies. To test an authenticated custom WordPress API endpoint externally, you must generate an Application Password via your WordPress user profile and pass it using Basic Auth in your API client.

Why does my route return a "rest_no_route" code?

This happens when the namespace or route string in your request URL does not exactly match what you defined in register_rest_route(). Double-check for trailing slashes, typos in the namespace, or mismatched regex patterns in your URL parameters.

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