The server will not accept the clients HTTP version.


  1. The server does not support, or refuses to support, the major version of HTTP that was used in the request message.
  2. 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.

Further Reading


505 HTTP Version Not Supported | The HTTP Working Group

505 HTTP Version Not Supported

MDN web docs

Upgrade header field

MDN web docs