What causes an HTTP 501 error and how do I fix it? or Getting an HTTP 501 - Not Implemented error. An

http 501 can be a pain. First, double-check your request headers. Missing Content-Type or Accept headers can sometimes trigger this.

If you’re on a shared host, some of them disable certain methods for "security." Might wanna contact support.

For debugging, I swear by Chrome DevTools or Fiddler. They’ll show you the raw request/response.