Flutter Operation was rejected while querying the subchild of doc in firestore

I'm working on an eCommerce app and working on a coupon system while creating a query I'm getting this error every time.

FirebaseException ([cloud_firestore/failed-precondition] Operation was rejected because the system is not in a state required for the operation's execution. If performing a query, ensure it has been indexed via the Firebase console.)

I tried to search the error but couldn't find the exact solution as some answers suggest that I have to create a collection index which I did but still getting the same error.

This how my query looks like:-

Future<void> fetchCouponCode(
    String couponCode,
    String userId,
    String priductCategory,
    String productIds,
) async {
   if (couponCode == null) {
      return;
   }
   if (userId == null) {
      return;
   }
   print(couponCode);
   var today = DateTime.now();
   await FirebaseFirestore.instance
      .collection('coupons')
      .where('code', isEqualTo: couponCode)
      .where('product_categories', isEqualTo: priductCategory)
      .where('customer_email', isEqualTo: 'all')
      .where('product_ids', arrayContainsAny: [productIds])
      // .where('constraints.BagConstraints.min_item', isGreaterThan: 1)
      .where('is_enabled', isEqualTo: true)
      .where('valid_from',
        isGreaterThanOrEqualTo: today)
      .get()
      .then((QuerySnapshot querySnapshot) {
          print('=========object=======');
          querySnapshot.docs.forEach((element) {
              print(element.get('discount'));
          });
          
       });
  }

This is how my coupon structure looks like

   var uuid = Uuid();
  {
    'coupon_id': uuid.v4(),
    'code': 'V710OFF',
    'description': 'Summer Sale',
    'discount': 40,
    'minimum_dicount': 30,
    'maximum_discount': 150,
    'discount_type': 'percent',
    'product_ids': ['3'],
    'date_created': DateTime.now(),
    'exclude_product_ids': 2,
    'product_categories': 't-shirts',
    'exclude_product_categories': '',
    'customer_email': 'all',
    'constraints': {
      'commonConstraints': {
        'uniqueId': uuid.v4(),
        'device_type': 'ios',
        'valid_from': DateTime.now(),
        'valid_until': DateTime.now().add(Duration(days: 10)),
        'usage_limit': 1,
        'usage_limit_per_user': 1,
        'total_usage': 10
      },
      'BagConstraints': {
        'uniqueId': uuid.v4(),
        'min_value': 120,
        'max_value': 3000,
        'min_item': 1,
        'max_item': 4,
      }
    },
    'is_enabled': true
  }

I need to check if the coupon is invalid date range. So shall I do inside querySnapshot.docs.forEach as this can be done but what if I have a similar issue with another collection. How do I query third-level docs or this can't be achieved right now?? Also I go through firestore documentation and youtube channel but couldn't find the solution

And this is how I query coupon

fetchCouponCode(
    'V710OFF', currentFirebaseUser.uid, 't-shirts', '3');