HTTP status codes / 5xx — Server errors
Server misconfiguration in content negotiation.
Transparent content negotiation ended in a loop: the chosen variant itself negotiates. A server configuration error, vanishingly rare in the wild.
Server-side fix only — the negotiation config references itself.
The fastest way to pin down a 506 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 · 505 HTTP Version Not Supported — or the full reference.
Build the request, send it, read status + headers + timing — on your iPhone. Free to start.