1. Install websocat with brew install websocat
2. Start the stack with docker compose up -d
3. Open a terminal window and run websocat ws://localhost:1932/listen?receiver=D
4. Open another terminal window and run curl http://localhost:1932/send -X POST -d '{"receiver": "D", "message": "sup dawg"}'

You should see the message from the last step appear in the websocket terminal window.