5×× SERVER ERROR
505 HTTP VERSION NOT SUPPORTED
The server does not support, or refuses to support, the major version of HTTP that was used in the request message.
The server is indicating that it is unable or unwilling to complete the request using the same major version as the client, as described in Section 2.6 of RFC7230, other than with this error message. The server SHOULD generate a representation for the 505 response that describes why that version is not supported and what other protocols are supported by that server.
505 HTTP VERSION NOT SUPPORTED Source: RFC7231 Section 6.6.6
505 CODE REFERENCES
Rails HTTP Status Symbol
Go HTTP Status Constant
Symfony HTTP Status Constant
Python2 HTTP Status Constant
Python3+ HTTP Status Constant
Python3.5+ HTTP Status Constant