HTTP headers / response header
Content-Encoding: gzip
Declares how the body bytes are compressed (gzip, br, zstd). The client must decode before parsing.
If you see binary garbage instead of JSON, you almost certainly received a compressed body and skipped decompression.
The fastest way to see what Content-Encoding is actually doing is to send the request and read both sides raw — ReqPad shows auto-generated and custom headers for every request, on all six protocols, with history. Related references: status codes · WWW-Authenticate · Transfer-Encoding · ETag · Last-Modified · Expires · Location
Build the request, send it, read raw headers and timing — from your iPhone. Free to start.