Sandbox Paypal payment Checkout using stored card Vault - paypal

Question

I am using Vault to stored credit card information to Paypal sandbox account which is done.
Now i want to integrate the payment process using stored credit card id. please guide how achieve this. Below are code block.
public class HomeController : Controller
{
public ActionResult Index()
{
//
PaypalCCModel ccmodel = new PaypalCCModel();
ccmodel.Number = "5555555555554444"; //"4111111111111111"; //"4012888888881881";// "4417119669820331"; // Visa
ccmodel.ExpireMonth = "11";
ccmodel.ExpireYear = "2021";
//ccmodel.cvv2 = "222";
ccmodel.Type = "MasterCard";
PaymentViaStoredCard(StoreCreditCardInPaypal(ccmodel));
return View();
}
// It return Vault Credit Card Id
private string StoreCreditCardInPaypal(PaypalCCModel ccmodel)
{
Address billingAddress = new Address();
billingAddress.city = "Johnstown";
billingAddress.country_code = "US";
billingAddress.line1 = "52 N Main ST";
billingAddress.postal_code = "43210";
billingAddress.state = "OH";
//Creating the CreditCard Object and assigning values
CreditCard credtCard = new CreditCard();
credtCard.expire_month = int.Parse(ccmodel.ExpireMonth);
credtCard.expire_year = int.Parse(ccmodel.ExpireYear);
credtCard.number = ccmodel.Number;
credtCard.type = ccmodel.Type.ToLower();
//credtCard.cvv2 = ccmodel.cvv2;
credtCard.first_name = "pankaj";
credtCard.last_name = "Kumar";
credtCard.billing_address = billingAddress;
try
{
//Getting the API Context to authenticate the call to Paypal Server
PayPal.Api.APIContext apiContext = Configuration.GetAPIContext();
Dictionary<string, string> headers = new Dictionary<string, string>();
//headers.Add("Content-Type", "application/json");
//headers.Add("Authorization", "Bearer "+ apiContext.AccessToken.ToString());
apiContext.HTTPHeaders = headers;
// Storing the Credit Card Info in the PayPal Vault Server
CreditCard createdCreditCard = credtCard.Create(apiContext);
//Saving the User's Credit Card ID returned by the PayPal
//You can use this ID for future payments via User's Credit Card
//SaveCardID(User.Identity.Name, createdCreditCard.id);
return createdCreditCard.id;
}
catch (PayPal.PayPalException ex)
{
//Logger.LogError("Error: " + ex.Message);
return "-1";
}
catch (Exception ex)
{
//Logger.LogError("Error: " + ex.Message);
}
return "-1";
}
public void PaymentViaStoredCard(string CardID)
{
// Preparing Item
Item item = new Item();
item.name = "Item Name";
item.currency = "USD";
item.price = "1";
item.quantity = "1";
item.sku = "sku-1123324";
List<Item> itms = new List<Item>();
itms.Add(item);
ItemList itemList = new ItemList();
itemList.items = itms;
//Here is the Credit Card detail which we need to use from our database
CreditCardToken credCardToken = new CreditCardToken();
//Here, we are assigning the User's Credit Card ID which we saved in Database
credCardToken.credit_card_id = CardID;
//Specify Payment Details
Details details = new Details();
details.shipping = "1";
details.subtotal = "1";
details.tax = "1";
//Specify the Total Amount
Amount amnt = new Amount();
amnt.currency = "USD";
// Total must be equal to the sum of shipping, tax and subtotal.
amnt.total = "3";
amnt.details = details;
//Create Transaction Object
Transaction tran = new Transaction();
tran.amount = amnt;
tran.description = "This is the recurring payment transaction";
tran.item_list = itemList;
//Adding the transaction above to the list
List<Transaction> transactions = new List<Transaction>();
transactions.Add(tran);
//Specifying the funding Instrument here.
//Notice that we are not using any credit card details here
//But we are using the Credit Card Object which has the Card ID
FundingInstrument fundInstrument = new FundingInstrument();
fundInstrument.credit_card_token = credCardToken;
//Adding the Funding Instrument to the list
List<FundingInstrument> fundingInstrumentList = new List<FundingInstrument>();
fundingInstrumentList.Add(fundInstrument);
//Specify the fundind Instrument List and Payment Method as Credit Card
//Because we are making the payment using the store Credit Card
Payer payr = new Payer();
payr.funding_instruments = fundingInstrumentList;
payr.payment_method = "credit_card";
//Finally Making payment Object and filling it with values
Payment pymnt = new Payment();
pymnt.intent = "sale";
pymnt.payer = payr;
pymnt.transactions = transactions;
try
{
//Getting the API Context to authenticate the Call to Paypal Server
PayPal.Api.APIContext apiContext = Configuration.GetAPIContext();
// Making the payment using a valid APIContext
Payment createdPayment = pymnt.Create(apiContext);
}
catch (PayPal.PayPalException ex)
{
//Logger.LogError("Error: " + ex.Message);
}
}
}
The PaymentViaStoredCard method is stored credit card information on PayPal sandbox vault and return vault Card id which is passed to PaymentViaStoredCard method to pay amount PayPal. But I am getting error in PaymentViaStoredCard method like internal server error.
The full error description is
{"name":"INTERNAL_SERVICE_ERROR","message":"An internal service error occurred.","information_link":"developer.paypal.com/docs/api/payments/…"}