505 HTTP Version Not Supported
HTTP response status code 505 HTTP Version Not Supported is a server error message that indicates the server is unwilling to process the HTTP request using the major version of HTTP that was used in the HTTP request message.
When the 505 HTTP Version Not Supported status code is received, it means that the server does not support the major protocol used by the HTTP request. The server is expected to generate a HTTP response indicating why the specific HTTP protocol is not supported and also list which HTTP protocols the server is willing to accept at this URI.
In the example, the client requests a resource and the server responds with a 505 HTTP Version Not Supported status code because it does not support HTTP/3.
GET / HTTP/3
HTTP/1.1 505 HTTP Version Not Supported
Content-Type: text/html; charset=UTF-8
<title>Protocol Not Supported<\title>
<p>HTTP/3 not supported. Please use HTTP/1.1.</p>
Apache HttpComponents Core
The 505 HTTP Version Not Supported status code is a server error that is generated when the server is unable or unwilling to process a HTTP request because it does not support the HTTP protocol that was used to submit it.