Google Script: Add guest to event (Google Calender) but it doesn't send a invitation email

Thats my code:

function addToEvent() {

 var guest = "";
 var calendar = '';
 var event = "";

 var cal = CalendarApp.getCalendarById(calendar);
 var theEvent = cal.getEventSeriesById(event); 

 theEvent.addGuest(guest); }

Everything works but it does not send an invitation mail to the guest.
I know it works with ( sendUpdates: "all" ) but I dont know how to add that here

Thanks in Advance!

Try the below code. I have tested it and it works for me.
Just make sure you have enabled the V3 of Calendar API in advanced services.

function addGuestAndSendNotification(calendarId, eventId, newGuestEmailAddress) {

  eventId = eventId.substring(0, eventId.indexOf('@google.com'));

  var event = Calendar.Events.get(calendarId, eventId);
  var attendees = event.attendees;
  if (!attendees) attendees = [];
  attendees.push({ email: newGuestEmailAddress });

  var resource = { attendees: attendees };
  var args = { sendUpdates: "all" };

  Calendar.Events.patch(resource, calendarId, eventId, args);
}