HTTP status codes / 4xx — Client errors
The server cannot meet the Expect header.
Sent when a server refuses the Expect: 100-continue handshake (or any Expect value). Some older servers and proxies simply do not support it.
Disable Expect: 100-continue in your client (cURL: -H "Expect:") and resend.
Server-side note: Send the request with an empty Expect header (cURL: -H "Expect:").
The fastest way to pin down a 417 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.
400 Bad Request · 401 Unauthorized · 402 Payment Required · 403 Forbidden · 404 Not Found · 405 Method Not Allowed — or the full reference.
Build the request, send it, read status + headers + timing — on your iPhone. Free to start.