HTTP status codes / 5xx — Server errors
510 Not Extended
The request lacks an extension the server requires.
What it means
From the abandoned HTTP Extension Framework (RFC 2774): the server demands further extension declarations. Effectively a museum piece.
Common causes
- Server demands HTTP extension declarations (abandoned RFC 2774) — meaning is service-specific
How to debug it
If a real service sends 510, consult its docs — the meaning is service-specific.
The fastest way to pin down a 510 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.
Related codes
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.
Reproduce that 510 in 10 seconds.
Build the request, send it, read status + headers + timing — on your iPhone. Free to start.