All HTTP Status Codes
501
Not Implemented
5xx Server Error
RFC 9110What it means
The server does not support the functionality required to fulfill the request. Common when the HTTP method is not recognized or not implemented.
Common causes
- Unsupported HTTP method (e.g., PATCH on old servers)
- Unimplemented API feature
- Missing server module
How to fix it
Check the API documentation. The server does not support this operation — contact the server operator or use a different method.
Test this status code live
Send real HTTP requests and inspect status codes directly in your browser.