501 Not Implemented

What does 501 Not Implemented mean?

The server does not support the functionality required to fulfil the request. It belongs to the 5xx Server Error class, which means the server failed to fulfil an apparently valid request. The problem is on the server side.

When do APIs return 501?

An HTTP method the server does not recognise, or a documented-but-unbuilt endpoint.

How to fix a 501 Not Implemented

Check the API documentation for whether the feature actually shipped in the version you are calling.

Reproduce a 501 response

The fastest way to understand a status code is to trigger one and read the full response. Open the API tester and send a request to https://httpbin.org/status/501 — you will see the 501 status along with every response header the server sent. Comparing those headers against a working request is often what reveals the cause.

When you are debugging a real endpoint, check the response headers as carefully as the body, and confirm you are using the right HTTP method for the operation.

Related 5xx status codes