Trouble using Provider

I've been trying trying to make the checkout show the total price of what's in the basket. But turns it's way more difficult than I thought.

The list userOrders holds all the user has put into the basket

https://ibb.co/DQwTyHC

Provider class: (Or what it's suppossed to be)

class TotalPrice with ChangeNotifier {
  int ordersTotalPrice = 0;

  int totalPrice() {
    final ordersTotalPrice =
        userOrders.fold(0, (sum, order) => sum + order.totalPrice);
    notifyListeners();
    return ordersTotalPrice;
  }
}

Food:

class Food {
  String imgUrl;
  String desc;
  String name;
  String waitTime;
  num score;
  int price;
  int quantity;
  List<Map<String, String>> ingredients;
  String about;
  bool highlight;
  Food(this.imgUrl, this.desc, this.name, this.waitTime, this.score, this.price,
      this.quantity, this.ingredients, this.about,
      {this.highlight = false});
}

CheckOut button

class _NextButtonState extends State<NextButton> {
  String getCurrency() {
    var format = NumberFormat.simpleCurrency(name: 'NGN');
    return format.currencySymbol;
  }

  @override
  Widget build(BuildContext context) {
    return userOrders.isNotEmpty
        ? Container(
            color: Colors.transparent,
            padding: const EdgeInsets.fromLTRB(10.0, 10.0, 5.0, 5.0),
            height: 60,
            width: double.infinity,
            child: ElevatedButton(
              style: ButtonStyle(
                shape: MaterialStateProperty.all<RoundedRectangleBorder>(
                  RoundedRectangleBorder(
                    borderRadius: BorderRadius.circular(18.0),
                    side: const BorderSide(color: Colors.transparent),
                  ),
                ),
              ),
              child: Text(
                '${getCurrency()}${context.watch<TotalPrice>().ordersTotalPrice}',
                style: const TextStyle(
                  fontWeight: FontWeight.bold,
                  fontSize: 18.0,
                ),
              ),
              onPressed: () {},
            ),
          )
        : Text('');
  }
}

Here, you introduced local variable so the field orderTotalPrice didn't get updated as you have

final ordersTotalPrice = userOrders.fold(0, (sum, order) => sum + order.totalPrice);

change this line as following

ordersTotalPrice = userOrders.fold(0, (sum, order) => sum + order.totalPrice);

Edited

Use AnimationBuilder to refresh the changed data in UI.

AnimatedBuilder(
            animation: context.read<TotalPrice>(),
           
            builder: (BuildContext context, Widget? child) {
              return Text('${context.read<TotalPrice>().ordersTotalPrice}');
            },
          )