Troubleshooting the Issue

First, ensure your WordPress installation is up-to-date. Outdated versions can sometimes have bugs that cause this error. Then, check your plugin settings. Specifically, verify that any plugins you're using are correctly configured to handle REST API requests and that they're not attempting to access resources that aren't available. Examine your theme's `functions.php` file for any custom code that might be interfering with the `wp_is_serving_rest_request()` function. Finally, try temporarily disabling plugins to isolate the cause.