Not FIX on the wire
Modern stacks wrap FIX — do not confuse the wrapper with the protocol.
| Payload | FIX? |
|---|---|
| `8=FIX.4.4 | 9=… |
POST /fix HTTP/1.1 + body above |
FIX in HTTP tunnel — body is FIX |
{"ClOrdID":"x","55":"EUR/USD"} |
No — JSON API |
| gRPC OrderRequest protobuf | No |
| FIX SBE binary encoding | FIX semantics, not tag=value wire |
4H engine speaks classic tag=value FIX over TCP in eval packages. Your capture file must show 8= to be wire FIX.