HTTP 501 — Not Implemented
5xx Server Error
What it means
The server does not support the functionality required to fulfil the request.
What to do about it
Usually means an HTTP method the server does not recognise at all. Check for a proxy sending an unusual method.
Where it sits
501 belongs to the 5xx family: The server failed to fulfil an apparently valid request. The fix is on the server side.
HTTP/1.1 501 Not ImplementedChecking it yourself
# see the status code and headers only
curl -sI https://example.com/path
# follow redirects and print each hop
curl -sIL -o /dev/null -w "%{http_code} %{url_effective}\n" https://example.com/path
# JavaScript
const r = await fetch(url);
console.log(r.status, r.statusText);