public override void PayPalPaymentViewController (PayPalPaymentViewController paymentViewController, PayPalPayment completedPayment)
{
//throw new NotImplementedException ();
Debug.WriteLine("PayPal Payment Success !");
paymentViewController.DismissViewController (true, () => {
// send completed confirmaion to your server
Debug.WriteLine ("Here is your proof of payment:" + completedPayment.Confirmation + "Send this to your server for confirmation and fulfillment.");
ResultText = completedPayment.Description;
});
}