HTTP 505 status code means a server doesn’t support the major HTTP version you’re requesting.
It happens when you specify a non-existent (e.g., HTTP/1.2) or unsupported (e.g., HTTP/3) HTTP protocol version in your request.
You might also encounter the 505 HTTP Version Not Supported status code if you send the valid and supported HTTP version to the server with trailing whitespace. According to the HTTP 1.1 spec, the version of the HTTP message should contain the string HTTP, followed by the forward slash, and the protocol version formatted as <major>.<minor>.
HTTP "/" DIGIT "." DIGIT
If you’re using the protocol version without a minor version (e.g., HTTP/2 or HTTP/3), you can omit the minor version part.