paypal Amount Total mismatch

问题

When I check in my website using Paypal it gives me this message: "Checkout Error - Amount total mismatch" I used Microsoft tutorial to implement PayPal:

https://docs.microsoft.com/en-us/aspnet/web-forms/overview/getting-started/getting-started-with-aspnet-45-web-forms/checkout-and-payment-with-paypal

I did exactly what it said I even did twice but somehow keep getting this error Appreciate your help Thanks

public partial class CheckoutReview : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            NVPAPICaller payPalCaller = new NVPAPICaller();

            string retMsg = "";
            string token = "";
            string PayerID = "";
            NVPCodec decoder = new NVPCodec();
            token = Session["token"].ToString();

            bool ret = payPalCaller.GetCheckoutDetails(token, ref PayerID, ref decoder, ref retMsg);
            if (ret)
            {
                Session["payerId"] = PayerID;

                var myOrder = new Order();
                myOrder.OrderDate = Convert.ToDateTime(decoder["TIMESTAMP"].ToString());
                myOrder.Username = User.Identity.Name;
                myOrder.FirstName = decoder["FIRSTNAME"].ToString();
                myOrder.LastName = decoder["LASTNAME"].ToString();
                myOrder.Address = decoder["SHIPTOSTREET"].ToString();
                myOrder.City = decoder["SHIPTOCITY"].ToString();
                myOrder.State = decoder["SHIPTOSTATE"].ToString();
                myOrder.PostalCode = decoder["SHIPTOZIP"].ToString();
                myOrder.Country = decoder["SHIPTOCOUNTRYCODE"].ToString();
                myOrder.Email = decoder["EMAIL"].ToString();
                myOrder.Total = Convert.ToDecimal(decoder["AMT"].ToString());

                // Verify total payment amount as set on CheckoutStart.aspx.
                try
                {
                    decimal paymentAmountOnCheckout = Convert.ToDecimal(Session["payment_amt"].ToString());
                    decimal paymentAmoutFromPayPal = Convert.ToDecimal(decoder["AMT"].ToString());
                    if (paymentAmountOnCheckout != paymentAmoutFromPayPal)
                    {
                        Response.Redirect("CheckoutError.aspx?" + "Desc=Amount%20total%20mismatch.");
                    }
                }
                catch (Exception)
                {
                    Response.Redirect("CheckoutError.aspx?" + "Desc=Amount%20total%20mismatch.");
                }

                // Get DB context.
                ProductContext _db = new ProductContext();

                // Add order to DB.
                _db.Orders.Add(myOrder);
                _db.SaveChanges();

                // Get the shopping cart items and process them.
                using (WingtipToys.Logic.ShoppingCartActions usersShoppingCart = new WingtipToys.Logic.ShoppingCartActions())
                {
                    List<CartItem> myOrderList = usersShoppingCart.GetCartItems();

                    // Add OrderDetail information to the DB for each product purchased.
                    for (int i = 0; i < myOrderList.Count; i++)
                    {
                        // Create a new OrderDetail object.
                        var myOrderDetail = new OrderDetail();
                        myOrderDetail.OrderId = myOrder.OrderId;
                        myOrderDetail.Username = User.Identity.Name;
                        myOrderDetail.ProductId = myOrderList[i].ProductId;
                        myOrderDetail.Quantity = myOrderList[i].Quantity;
                        myOrderDetail.UnitPrice = myOrderList[i].Product.UnitPrice;

                        // Add OrderDetail to DB.
                        _db.OrderDetails.Add(myOrderDetail);
                        _db.SaveChanges();
                    }

                    // Set OrderId.
                    Session["currentOrderId"] = myOrder.OrderId;

                    // Display Order information.
                    List<Order> orderList = new List<Order>();
                    orderList.Add(myOrder);
                    ShipInfo.DataSource = orderList;
                    ShipInfo.DataBind();

                    // Display OrderDetails.
                    OrderItemList.DataSource = myOrderList;
                    OrderItemList.DataBind();
                }
            }
            else
            {
                Response.Redirect("CheckoutError.aspx?" + retMsg);
            }
        }
    }

    protected void CheckoutConfirm_Click(object sender, EventArgs e)
    {
        Session["userCheckoutCompleted"] = "true";
        Response.Redirect("~/Checkout/CheckoutComplete.aspx");
    }
}

来源：https://stackoverflow.com/questions/50452365/paypal-amount-total-mismatch