A 505 HTTP Version Not Supported error is a webserver’s code for: "I don't support the version of the HTTP protocol that your client used.".

How do I fix or troubleshoot a 505 Error?

Common steps include reloading the page in your browser, checking for typos in the URL, verifying server status, clearing browser cache or cookies, and contacting the website owner or server administrator if the error persists.

505 Error | Error-Message.Net

A 505 HTTP Version Not Supported error indicates that the server does not support, or refuses to support, the major version of HTTP that was used in the request message.

HTTP has evolved through several major revisions—HTTP/1.0, HTTP/1.1, HTTP/2, and HTTP/3. If an obsolete or unsupported protocol version is sent to a server, it returns 505.

Determining why

Modern browsers automatically negotiate supported HTTP versions. A 505 error is almost always caused by:

An ancient client tool or outdated custom network script.
A corrupted request string where the protocol version at the end of the request line was malformed.

Steps you could possibly take:

Update your browser - Ensure you are using a modern browser version.
If you are developing custom network software:
- Verify that your client requests specify a standard supported protocol such as HTTP/1.1 or negotiate h2 via ALPN.

Source: RFC 9110 Section 15.6.6 (HTTP Semantics)