501 🌐 HTTP

HTTP 501 Not Implemented

The server doesn’t support the functionality (usually the HTTP method) needed to fulfil the request.

Seen on: Nginx REST API

Meaning

Unlike 405 (method known but not allowed on this URL), 501 means the server doesn’t recognise or support the method at all — e.g. PATCH or a WebDAV method on an old server/proxy. Some APIs also return it for features that are planned but not built.

Common causes

  • Unsupported HTTP method (PATCH, PROPFIND, custom verbs) on the server or a proxy
  • Typo in the method name
  • Endpoint stub returning 501 for unbuilt features
  • Old proxies stripping or rejecting newer methods

⚡ Quick fix

  1. Check the method spelling and use a standard method
  2. Use POST with an override header if a proxy blocks PATCH (X-HTTP-Method-Override)
  3. Upgrade/configure the server or proxy to pass the method through

Detailed fix by platform

Nginx

  1. Nginx returns 501 for unknown methods only in rare builds; more often a load balancer or WAF in front is responsible — test the origin directly.

REST API

  1. Return 405 + Allow header for known-but-unsupported methods; reserve 501 for truly unimplemented features.

How to diagnose

  1. Method — Which method was sent?
  2. Layer — Which hop returned 501?
  3. Support — Does the server support that method?

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