Await inside For Loop not working in initState function

I am trying to insert multiple records in initState() into the database using for loop as below:

void _insertManyAttendees() async {
    for (var i = 0; i < numberOfPeople; i++) {
      Map<String, dynamic> row = {'name': 'Attendee $i', 'billId': billId};
      await LocalStorageService.instance.insert(row, 'attendees');
    }
  }

However the function above only inserts one record to the database when it actually supposed to insert multiple records.

my initState() function:

@override
  void initState() {
    super.initState();
    // 1. Get number of attendees
    numberOfPeople =
        Provider.of<BillData>(context, listen: false).numberOfPeople;

    // 2. ID of new record in database
    billId = Provider.of<BillData>(context, listen: false).id;
    debugPrint('inserted Row ID in input_attendees_screen: $billId');

    WidgetsBinding.instance.addPostFrameCallback((_) {
      // 3. Create new records in ATTENDEES table based on number of people
      _insertManyAttendees();

      // 4. Find all ATTENDEES based on billId
      _findManyAttendees(billId);

      _findAllAttendees();
    });
  }

_findManyAttendees(billId) always return only 1 record during the initial insertion but in the next run, it always return the correct number of records.

Wondering what went wrong. Many thanks in advance for the help.

Include Future<void>:

Future<void> _insertManyAttendees() async {
  for (var i = 0; i < numberOfPeople; i++) {
    Map<String, dynamic> row = {'name': 'Attendee $i', 'billId': billId};
    await LocalStorageService.instance.insert(row, 'attendees');
  }
}

Call the method using await:

await _insertManyAttendees();