Fulfill Purchase

To implement the fulfill purchase API using the SDK, implement one abstract method from the PurchaseController class: ProcessFulfillPurchase.

         /// <summary>
         /// Processes Fulfill Purchase requests.
         /// </summary>
         /// <returns>A <see cref="Task{T}"/> of <see cref="FulfillPurchaseResposne"/> or an exception if bill once purchases are not supported.</returns>
         protected override Task<FulfillPurchaseResposne> ProcessFulfillPurchase(PurchaseRequest purchaseRequest);
request);