首次成功测试asp mvc后，Paypal失败了

Question

我正在尝试将PayPal应用到我的网络应用中。

PayPal付款第一次正常运作！

但如果我第二次尝试，那就失败了。我可以只测试一次???

当PayPal成功时，我会看到以下链接：

https://localhost:44333/Paypal/PaymentWithPayPal?guid=94987&paymentId=PAY-1DM32358RW0519317LDPKCYY&token=EC-1G993722W11620224&PayerID=8QXDDJEKRZKZW

当PayPal失败时，我会看到以下链接：

https://localhost:44333/Paypal/PaymentWithPayPal?guid=52246&paymentId=PAY-9V465873R0219235GLDPKDNA&token=EC-1F105391KF572764B&PayerID=8QXDDJEKRZKZW

这是我的 PayPalController ：

public class PayPalController : Controller
{
    [Authorize]

    // GET: PayPal
    public ActionResult Index()
    {
        return View();
    }

    public ActionResult PaymentWithPaypal()
    {
        //getting the apiContext as earlier
        APIContext apiContext = Configuration.GetAPIContext();

        try
        {
            string payerId = Request.Params["PayerID"];

            if (string.IsNullOrEmpty(payerId))
            {
                //this section will be executed first because PayerID doesn't exist
                //it is returned by the create function call of the payment class

                // Creating a payment
                // baseURL is the url on which paypal sendsback the data.
                // So we have provided URL of this controller only
                string baseURI = Request.Url.Scheme + "://" + Request.Url.Authority +
                            "/Paypal/PaymentWithPayPal?";

                //guid we are generating for storing the paymentID received in session
                //after calling the create function and it is used in the payment execution

                var guid = Convert.ToString((new Random()).Next(100000));

                //CreatePayment function gives us the payment approval url
                //on which payer is redirected for paypal account payment

                var createdPayment = this.CreatePayment(apiContext, baseURI + "guid=" + guid);

                //get links returned from paypal in response to Create function call

                var links = createdPayment.links.GetEnumerator();

                string paypalRedirectUrl = null;

                while (links.MoveNext())
                {
                    Links lnk = links.Current;

                    if (lnk.rel.ToLower().Trim().Equals("approval_url"))
                    {
                        //saving the payapalredirect URL to which user will be redirected for payment
                        paypalRedirectUrl = lnk.href;
                    }
                }

                // saving the paymentID in the key guid
                Session.Add(guid, createdPayment.id);

                return Redirect(paypalRedirectUrl);
            }
            else
            {
                // This section is executed when we have received all the payments parameters

                // from the previous call to the function Create

                // Executing a payment

                var guid = Request.Params["guid"];

                var executedPayment = ExecutePayment(apiContext, payerId, Session[guid] as string);

                if (executedPayment.state.ToLower() != "approved")
                {
                    return View("FailureView");
                }
            }
        }
        catch (Exception ex)
        {
            Logger.Log("Error" + ex.Message);
            return View("FailureView");
        }

        return View("SuccessView");
    }

    private PayPal.Api.Payment payment;

    private Payment ExecutePayment(APIContext apiContext, string payerId, string paymentId)
    {
        var paymentExecution = new PaymentExecution() { payer_id = payerId };
        this.payment = new Payment() { id = paymentId };
        return this.payment.Execute(apiContext, paymentExecution);
    }

    private Payment CreatePayment(APIContext apiContext, string redirectUrl)
    {
        var userId = User.Identity.GetUserId();
        var userEmail = User.Identity.GetUserName();
        //similar to credit card create itemlist and add item objects to it
        var itemList = new ItemList() { items = new List<Item>() };

        itemList.items.Add(new Item()
        {
            name = "Premium Monthly $99.00",
            currency = "USD",
            price = "99",
            quantity = "1",
            description = userEmail + " Pays Premium Monthly $99.00 on " + DateTime.Now.ToString("F")
        });

        var payer = new Payer() { payment_method = "paypal" };

        // Configure Redirect Urls here with RedirectUrls object
        var redirUrls = new RedirectUrls()
        {
            cancel_url = redirectUrl,
            return_url = redirectUrl
        };

        // similar as we did for credit card, do here and create details object
        var details = new Details()
        {
            subtotal = "99.00"
        };

        // similar as we did for credit card, do here and create amount object
        var amount = new Amount()
        {
            currency = "USD",
            total = "99.00", // Total must be equal to sum of shipping, tax and subtotal.
            details = details
        };

        var transactionList = new List<Transaction>();

        transactionList.Add(new Transaction()
        {
            description = userEmail + "Paid Premium Monthly $99.00 on " + DateTime.Now.ToString("F"),
            invoice_number = "890918",
            amount = amount,
            item_list = itemList
        });

        this.payment = new Payment()
        {
            intent = "sale",
            payer = payer,
            transactions = transactionList,
            redirect_urls = redirUrls
        };

        // Create a payment using a APIContext
        return this.payment.Create(apiContext);

    }
}

请帮忙！