services.AddScoped<IShoppingCartService, MyShoppingCartService>();

    public class MyShoppingCartService : ShoppingCartService ,IShoppingCartService
    {
        public MyShoppingCartService(IWorkContext workContext, IProductService productService, IProductAttributeParser productAttributeParser, ICheckoutAttributeParser checkoutAttributeParser, ICustomerService customerService, IMediator mediator, IUserFieldService userFieldService, IProductReservationService productReservationService, IShoppingCartValidator shoppingCartValidator, ShoppingCartSettings shoppingCartSettings) : base(workContext, productService, productAttributeParser, checkoutAttributeParser, customerService, mediator, userFieldService, productReservationService, shoppingCartValidator, shoppingCartSettings)
        {
        }

        public override Task<IList<string>> AddToCart(Customer customer, string productId, ShoppingCartType shoppingCartType, string storeId,
            string warehouseId = null, IList<CustomAttribute> attributes = null, double? customerEnteredPrice = null,
            DateTime? rentalStartDate = null, DateTime? rentalEndDate = null, int quantity = 1,
            bool automaticallyAddRequiredProductsIfEnabled = true, string reservationId = "", string parameter = "",
            string duration = "", bool getRequiredProductWarnings = true)
        {
            return base.AddToCart(customer, productId, shoppingCartType, storeId, warehouseId, attributes, customerEnteredPrice, rentalStartDate, rentalEndDate, quantity, automaticallyAddRequiredProductsIfEnabled, reservationId, parameter, duration, getRequiredProductWarnings);
        }
    }

public class StartupApplication : IStartupApplication
    {
        public void ConfigureServices(IServiceCollection services, IConfiguration configuration)
        {
            services.AddScoped<IShoppingCartService, MyShoppingCartService>();
        }

        public void Configure(IApplicationBuilder application, IWebHostEnvironment webHostEnvironment)
        {

        }

        public int Priority => 102;

        public bool BeforeConfigure => false;
    }