Unity IAP Slow Card Handling

I am using Unity IAP 4.1.4.

As you know there are 4 different test cards on purchase testing. My question is what should I do when payment is slow? If user quits the game before payment validated I can't approve the payment and purchase is pending. Is there any way to handle slow payments?

 public class IAPManager : MonoBehaviour
 {
     private string coin250k = "//";
     private string coin500k = "//";
 
     public void OnPurchaseComplete(Product product)
     {
         var validator = new CrossPlatformValidator(GooglePlayTangle.Data(),
 AppleTangle.Data(), Application.identifier);
 
         bool ValidPurchase = false;
 
         try
         {
             // On Google Play, result has a single product ID.
             // On Apple stores, receipts contain multiple products.
             var result = validator.Validate(product.receipt);
             // For informational purposes, we list the receipt(s)
             Debug.Log("Receipt is valid. Contents:");
 
             foreach (IPurchaseReceipt productReceipt in result)
             {
                 Debug.Log(productReceipt.productID);
                 Debug.Log(productReceipt.purchaseDate);
                 Debug.Log(productReceipt.transactionID);
 
                 GooglePlayReceipt google = productReceipt as GooglePlayReceipt;
                 if (null != google)
                 {
                     // This is Google's Order ID.
                     // Note that it is null when testing in the sandbox
                     // because Google's sandbox does not provide Order IDs.
                     ValidPurchase = true;
 
                     Debug.Log(" google transaction" + google.transactionID);
                     Debug.Log(" google transaction" + google.purchaseState);
                     Debug.Log(" google transaction" + google.purchaseToken);
                 }
 
                 AppleInAppPurchaseReceipt apple = productReceipt as AppleInAppPurchaseReceipt;
                 if (null != apple)
                 {
                     ValidPurchase = true;
                     Debug.Log(" apple transaction1" + apple.originalTransactionIdentifier);
                     Debug.Log(" apple transaction2" + apple.subscriptionExpirationDate);
                     Debug.Log(" apple transaction3" + apple.cancellationDate);
                     Debug.Log(" apple transaction4" + apple.quantity);
                 }
             }
         }
         catch (IAPSecurityException)
         {
             Debug.Log("Invalid receipt, not unlocking content");
             ValidPurchase = false;
         }
         //product.receipt;
         if (ValidPurchase)
         {
             if (product.definition.id == coin250k)
             {
                 //
             }
             else if (product.definition.id == coin500k)
             {
                 //
             }
         }
 
     }    
     public void OnPurchaseFailed(Product product, PurchaseFailureReason reason)
     {
         Debug.Log(product.definition.id + " failed because: "+ reason);
     }
 }