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501 Not Implemented

The HyperText Transfer Protocol (HTTP) 501 Not Implemented server error response code indicates that the request method is not supported by the server and cannot be handled. The only methods that servers are required to support (and therefore that must not return this code) are GET and HEAD.

Notes:

A 501 error is not something you can fix, but requires a fix by the web server you are trying to access.
A 501 response is cacheable by default.

Status

501 Not Implemented

Specifications

Specification	Title
RFC 7231, section 6.6.2: 501 Not Implemented	Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content

Browser compatibilityUpdate compatibility data on GitHub

The information shown below has been pulled from MDN's GitHub (https://github.com/mdn/browser-compat-data).

	Desktop
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari
Basic support	Yes	Yes	Yes	Yes	Yes	Yes

	Mobile
	Android webview	Chrome for Android	Edge Mobile	Firefox for Android	Opera for Android	iOS Safari	Samsung Internet
Basic support	Yes	Yes	Yes	Yes	Yes	Yes	Yes

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https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/501