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Description trigger modem to inform on RF that the user is typing a message
curl -X POST http://localhost:5000/modem/fec_is_writing
This API uses the following error codes:
400 Bad Request: The request was malformed or missing required parameters.
404 Not Found: The requested resource was not found.
500 Internal Server Error: An unexpected error occurred on the server.
503 Modem not running: Modem not running.