code: public void addAlert(String alertMessage) throws JSONException {
  		String previousAlert = getCompatibleProperty("alert", String.class, "A custom alert (\"%s\") was already added to this payload");
  		logger.debug("Adding alert [" + alertMessage + "]" + (previousAlert != null ? " replacing previous alert [" + previousAlert + "]" : ""));
  		put("alert", alertMessage, this.apsDictionary, false);
  	}
docs: Add a simple alert message.
  Note: you cannot add a simple and a custom alert in the same payload.
  
  @param alertMessage the alert's message
  @throws JSONException