HTTP status codes / 5xx — Server errors
The server refuses the HTTP version of the request.
The protocol version in the request line is not supported. Practically extinct, occasionally produced by ancient servers or hand-crafted requests.
Force HTTP/1.1 in your client and retry.
Server-side note: Force HTTP/1.1 in the client.
The fastest way to pin down a 505 is to reproduce the exact request and inspect what actually went over the wire — status, headers, timing and body, without your app code in the way. That is what an API client is for; ReqPad does it from your phone, with every request saved to history.
500 Internal Server Error · 501 Not Implemented · 502 Bad Gateway · 503 Service Unavailable · 504 Gateway Timeout · 506 Variant Also Negotiates — or the full reference.
Build the request, send it, read status + headers + timing — on your iPhone. Free to start.