code below

insert_calendar.dart

//inserir evento
Future<dynamic> insertEvent(CalendarStore calendarStore) async {

  Map<String, String> eventData;

  String calendarId;
  v3.Event event = v3.Event();

  event.summary = calendarStore.title;
  event.description = calendarStore.description;
  event.attendees = calendarStore.destiny;
  event.location = calendarStore.location;

  if (calendarStore.hasConferenceSupport) {
    v3.ConferenceData conferenceData = v3.ConferenceData();
    v3.CreateConferenceRequest conferenceRequest = v3.CreateConferenceRequest();
    conferenceRequest.requestId =
        "${DateTime.parse(calendarStore.startTime).millisecondsSinceEpoch}-${DateTime.parse(calendarStore.endTime).millisecondsSinceEpoch}";
    conferenceData.createRequest = conferenceRequest;

    event.conferenceData = conferenceData;
  }

  v3.EventDateTime start = new v3.EventDateTime();
  start.dateTime = DateTime.parse(calendarStore.startTime);
  start.timeZone = "GMT-03:00";
  event.start = start;

  v3.EventDateTime end = new v3.EventDateTime();
  end.timeZone = "GMT-03:00";
  end.dateTime = DateTime.parse(calendarStore.endTime);
  event.end = end;

  try {
    await clientViaUserConsent(
            calendarStore.clientID, calendarStore.scopes, prompt)
        .then((AuthClient client) { //como criar isso sem clientViaUserConsent? :(
      var calendar = v3.CalendarApi(client);
      calendar.events
          .insert(event, calendarId,
              conferenceDataVersion:
                  calendarStore.hasConferenceSupport ? 1 : 0,
              sendUpdates:
                  calendarStore.shouldNotifyAttendees ? "all" : "none")
          .then((value) {
        print("Event Status: ${value.status}");
        if (value.status == "confirmed") {
          String joiningLink;
          String eventId;

          eventId = value.id;

          if (calendarStore.hasConferenceSupport) {
            joiningLink =
                "https://meet.google.com/${value.conferenceData.conferenceId}";
            calendarStore.setUrl(joiningLink);
          }

          eventData = {'id': eventId, 'link': joiningLink};

          print('Event added to Google Calendar');
          calendarStore.setEventDatabase(eventId);
        } else {
          print("Unable to add event to Google Calendar");
        }
      });
    }
  } catch (e) {
    print('Error creating event \n\n\n$e');
  }
  return eventData;
}

dynamic prompt(String url) async {
  print("Please go to the following URL and grant access:");
  print("  => $url");
  print("");

  if (await canLaunch(url)) {
    await launch(url);
  } else {
    throw 'Could not launch $url';
  }
}