code: public void reply(MessageEnvelope envelope) {
  		FbBotMillResponse response = createResponse(envelope);
  		if (response != null) {
  			// If the response is valid, replies to it.
  			if (validate(response)) {
  				FbBotMillNetworkController.postJsonMessage(response);
  			}
  		}
  	}
docs: Method which defines the reply flow.
  
  @param envelope
  the current callback message