WasItemPurchased.cs

   protected async Task<PurchaseResult> WasItemPurchased(string productId, ItemType type)
        {

            var billing = CrossInAppBilling.Current;
            try
            {
                var connected = await billing.ConnectAsync(type);

                if (!connected)
                {
                    //Couldn't connect
                    return new PurchaseResult(PurchaseResultState.ConnectionIssue, null);

                }

                //check purchases
                var purchases = await billing.GetPurchasesAsync(type);
                purchases = purchases.ToArray();

                var purchase = purchases?.FirstOrDefault(p => p.ProductId == productId);
                //check for null just incase
                if (purchase != null)
                {
                    //Purchase restored
                    return new PurchaseResult(PurchaseResultState.Success, purchase);

                }
                else
                {
                    //no purchases found
                    return new PurchaseResult(PurchaseResultState.Failed, null);

                }
            }
            catch (InAppBillingPurchaseException purchaseEx)
            {

                    Logger.Error("StoreServiceBase.PurchaseInApp InAppBillingPurchaseException", purchaseEx);

                throw purchaseEx;

            }
            catch (Exception ex)
            {
                Logger.Error("StoreServiceBase.PurchaseInApp Exception", ex);

                throw ex;

                //Something has gone wrong
            }
            finally
            {
                await billing.DisconnectAsync();
            }

            return new PurchaseResult(PurchaseResultState.Failed, null);
        }