HTTP status codes / 4xx — Client errors
The requested byte range is outside the resource.
A Range request asked for bytes the resource does not have (e.g. resuming a download past the end of a file that changed). Content-Range in the response reports the actual size.
Clear the partial file / stored offset and restart the download from zero.
Server-side note: Discard the partial file and stored offset; restart from byte 0.
The fastest way to pin down a 416 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.