How to Fix 501 Not Implemented Error
What 501 Not Implemented means
HTTP status 501 is the server saying, in effect, that it does not know how to do what was asked. In practice, the problem is almost always the request method: the everyday methods GET and POST work fine, but a request using PUT, DELETE, PATCH, OPTIONS, or a custom method reaches a server that was never configured to handle it, so the server answers 501 instead of carrying out the action.
That is different from a 404, where the page does not exist, and from a 405, where the method is known but not allowed for that one resource. With a 501, the capability itself is missing — the server software is too old, a config rule blocks the method, a proxy strips it on the way through, or the API endpoint was left as a placeholder that was never actually built. Visitors usually hit this when submitting a form, saving an edit, uploading a file, or using an app feature that talks to an API, rather than when simply opening a page.
Common causes
- Outdated server software or a missing module: an old web server build or a disabled handler does not recognize newer or less common request methods.
- A proxy or CDN altering the request: a load balancer, reverse proxy, or CDN may convert, block, or drop PUT, DELETE, and PATCH requests before they reach the application.
- An API route that was never implemented: the endpoint exists in documentation or in a client app, but the server code behind it is a stub that returns 501 by design.
- Server config blocking the method: Limit, LimitExcept, or limit_except rules, security plugins, or firewall rules can reject certain methods for a path or for the whole site.
- A stale link or an outdated client: an old bookmark, a cached page, or an outdated app can send a request to a feature the current server no longer offers, or in a format it no longer accepts.
How to fix the 501 Not Implemented error — step by step
Steps 1 and 2 are for visitors. Steps 3 through 6 are for site owners.
- Reload and check the address. Press Ctrl + R (or Cmd + R on a Mac) and try the page again, since a one-off failed request can produce a misleading status code. Check the address carefully: a mistyped path, a stale bookmark, or a link to a removed feature can send a request the server was never built to handle. If the error appears after clicking a button or submitting a form, try the same action once more before assuming the whole site is broken.
- Try another browser, device, or network. Open the same page in an incognito window (Ctrl + Shift + N) or a different browser to rule out a bad cached page or a browser extension interfering with the request. Also try your phone on mobile data: if the page works there, the problem may be a proxy, VPN, or corporate network that is altering or blocking the request method before it reaches the server. If the error follows you everywhere, it is almost certainly a server-side problem.
- Site owner: find the exact request in the logs. Open your web server error log and access log and look for the 501 entries: they show the request method, the URL, and the time, which tells you whether the failing requests are PUT, DELETE, PATCH, or a custom method. On Apache, check the error log in your hosting panel or at /var/log/apache2/error.log; on Nginx, check /var/log/nginx/error.log. Do not guess at the fix until you know which method and which path the server is rejecting.
- Site owner: enable the method in your server config. A server or security rule may be blocking the method outright. In Apache, look for Limit or LimitExcept blocks in .htaccess or your virtual host that deny the method, and remove or widen them for the paths that need it. In Nginx, check location blocks for limit_except directives and for if conditions that return 501 for non-GET requests. After any change, test the config with apachectl configtest or nginx -t, then reload with sudo systemctl reload apache2 or sudo systemctl reload nginx.
- Site owner: update the server and its modules. An old server build, a missing module, or an outdated CGI handler may simply not know the method being requested. Update your web server package, make sure the modules your application needs are enabled (for example, mod_proxy for proxied requests), and confirm your application framework version supports the method in use. Restart the server after the update with sudo systemctl restart apache2 or sudo systemctl restart nginx, then retest the same request.
- Site owner: check the proxy and finish the API route. If a CDN, load balancer, or reverse proxy sits in front of your app, confirm it forwards the original method unchanged: some proxies convert unusual methods to GET or drop them entirely, which makes a working backend look unimplemented. In Cloudflare or your proxy settings, check for method restrictions and for rules that block PUT, DELETE, or PATCH. Finally, confirm the API route itself is actually implemented: a placeholder route that returns 501 by design needs real handler code, not a server tweak.
Did this fix it? Quick checklist
- The page or API action completes without the 501 error
- It works in an incognito window and on another network
- The server log no longer shows 501 entries for that method and path
- The proxy forwards the original request method unchanged
If 501s appear only for one feature — say, file uploads or account edits — while the rest of the site works, the fault is almost certainly that one route or one config rule, not the whole server. Fix that route first and retest it in isolation with a tool like curl, for example curl -X PUT with the same URL, before declaring the site fixed. Persistent 501s right after a server migration usually mean a module or config rule did not carry over: compare the old server config against the new one line by line.
Frequently asked questions
What does a 501 Not Implemented error mean?
It means the server does not recognize or does not support the functionality needed to fulfill the request, most often the HTTP method used, such as PUT, DELETE, or PATCH. The server understood the request well enough to answer, but it has no implementation for that kind of request.
Is a 501 error my fault as a visitor?
Almost never. A 501 is a server-side problem: the server, proxy, or application is not set up to handle that request. As a visitor you can reload, try another browser or network, and report the error to the site owner, but the real fix has to happen on the server.
What is the difference between 501 and 405 errors?
A 405 Method Not Allowed error means the method is known but not allowed for that specific resource, for example POST to a read-only page. A 501 Not Implemented error means the server does not support that method or feature at all, anywhere in its current setup.
How do I fix 501 errors on my own server or API?
Find the failing method and path in your server logs, remove config rules that block that method, update the server and its modules, confirm your proxy forwards the method unchanged, and make sure the API route is actually implemented with real handler code.