What does HTTP 505 mean?
The server does not support the HTTP version used in the request.
Common causes and when you see it
Very old or very new clients talking to a limited server.
How to fix or handle it
Use HTTP/1.1 or HTTP/2.
Test it yourself
Send a request with the online API tester, inspect the response with the HTTP header checker, or host an endpoint that returns 505 with the mock API generator to see how your app reacts.
Server errors hurt users and SEO. Monitor your endpoints so you know about 505 responses before your customers do.
HTTP 505 questions
The server does not support the HTTP version used in the request.
Very old or very new clients talking to a limited server.
Use HTTP/1.1 or HTTP/2.