code: public static void setGetStartedButton(String payload) {
  		if (payload == null || "".equals(payload)) {
  			logger.error("FbBotMill validation error: Get Started Button payload can't be null or empty!");
  			return;
  		}
  		Button button = new PostbackButton(null, ButtonType.POSTBACK, payload);
  		List<Button> buttonList = new ArrayList<Button>();
  		buttonList.add(button);
  		CallToActionsRequest request = new CallToActionsRequest(
  				ThreadState.NEW_THREAD, buttonList);
  		FbBotMillNetworkController.postThreadSetting(request);
  	}
docs: Sets the Get Started Button for the bot. The Get Started button is only
  rendered the first time the user interacts with a the Page on Messenger.
  When this button is tapped, the defined payload will be sent back with a
  postback received callback.
  
  @param payload
  the payload to return when the button is tapped.
  @see <a href=
  "https://developers.facebook.com/docs/messenger-platform/thread-settings/get-started-button"
  >Facebook's Get Started Button Documentation</a>