PayPal.Api.Payment.Execute C# (CSharp) Method

        public Payment Execute(APIContext apiContext, PaymentExecution paymentExecution)
        {
            return Payment.Execute(apiContext, this.id, paymentExecution);
        }

        public ActionResult PaymentWithPayPal(string donationAmt)
        {          
            //OAuthTokenCredential tokenCredential = new OAuthTokenCredential("AeJs4Inwk1Pn8ZNhkWiSLwerx4K64E1PD5TtL4FF7XImtEZ29aAWBTxYOVIBWxEXlW6FycnBz3U7J8jQ", "ENerw7v3F1YT1w5YRYHRPCbjfVSpAbvHVTJFfqc0jWPyeq8hcgmvaZn-1T1WzklDVqw7Pd7MGp3KEQXO");
            //string accessToken = tokenCredential.GetAccessToken();

            // Get a reference to the config
            var config = ConfigManager.Instance.GetProperties();

            // Use OAuthTokenCredential to request an access token from PayPal
            var accessToken = new OAuthTokenCredential(config).GetAccessToken();
            var apiContext = new APIContext(accessToken);

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

                if (string.IsNullOrEmpty(payerId))
                {

                    // ###Items
                    // Items within a transaction.
                    Item item = new Item();
                    item.name = "Item Name";
                    item.currency = "USD";
                    item.price = donationAmt;
                    item.quantity = "1";
                    item.sku = "sku";

                    List<Item> itms = new List<Item>();
                    itms.Add(item);
                    ItemList itemList = new ItemList();
                    itemList.items = itms;

                    // ###Payer
                    // A resource representing a Payer that funds a payment
                    // Payment Method
                    // as `paypal`
                    Payer payr = new Payer();
                    payr.payment_method = "paypal";
                    Random rndm = new Random();
                    var guid = Convert.ToString(rndm.Next(100000));

                    string baseURI = Request.Url.Scheme + "://" + Request.Url.Authority + "/Donations/DonationSuccessView?";

                    // # Redirect URLS
                    RedirectUrls redirUrls = new RedirectUrls();
                    redirUrls.cancel_url = baseURI + "guid=" + guid;
                    redirUrls.return_url = baseURI + "guid=" + guid;

                    // ###Details
                    // Let's you specify details of a payment amount.
                    Details details = new Details();
                    details.tax = "0";
                    details.shipping = "0";
                    details.subtotal = donationAmt;

                    // ###Amount
                    // Let's you specify a payment amount.
                    Amount amnt = new Amount();
                    amnt.currency = "USD";
                    // Total must be equal to sum of shipping, tax and subtotal.
                    amnt.total = donationAmt + ".00";
                    amnt.details = details;

                    // ###Transaction
                    // A transaction defines the contract of a
                    // payment - what is the payment for and who
                    // is fulfilling it. 
                    List<Transaction> transactionList = new List<Transaction>();
                    Transaction tran = new Transaction();
                    tran.description = "Donation";
                    tran.amount = amnt;
                    tran.item_list = itemList;
                    // The Payment creation API requires a list of
                    // Transaction; add the created `Transaction`
                    // to a List
                    transactionList.Add(tran);

                    // ###Payment
                    // A Payment Resource; create one using
                    // the above types and intent as `sale` or `authorize`
                    payment = new Payment();
                    payment.intent = "sale";
                    payment.payer = payr;
                    payment.transactions = transactionList;
                    payment.redirect_urls = redirUrls;

                    var createdPayment = payment.Create(apiContext);
                    string paypalRedirectUrl = null;
                    var links = createdPayment.links.GetEnumerator();
                    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
                {
                    var guid = Request.Params["guid"];
                    var paymentId = Session[guid] as string;
                    var paymentExecution = new PaymentExecution() { payer_id = payerId };
                    var pymnt = new Payment() { id = paymentId };
                    var executedPayment = pymnt.Execute(apiContext, paymentExecution);
                }
            }
            catch (Exception e)
            {
                string error = e.ToString();
                return View("DonationFailureView");
            }
            return View("DonationSuccessView");
        }