HTTP status codes / 2xx — Success
Delta encoding: the response is a diff against a previous version.
Part of RFC 3229 instance manipulation: the server returns a delta relative to a cached version instead of the full resource. Practically extinct on the public web.
If you ever see this, the server supports delta encoding and your client asked for it via A-IM.
The fastest way to pin down a 226 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.
200 OK · 201 Created · 202 Accepted · 203 Non-Authoritative Information · 204 No Content · 205 Reset Content — or the full reference.
Build the request, send it, read status + headers + timing — on your iPhone. Free to start.