private async Task GetRatesAsync()
        {
            // We're now fetching the rates from Shopify. This will will calculate shipping rates very similarly to how our web checkout.
            // We then turn our BUYShippingRate objects into PKShippingMethods for Apple to present to the user.

            if (checkout.RequiresShipping)
            {
                try
                {
                    BuyClient.ShippingRatesForCheckoutResult result;
                    while ((result = await client.GetShippingRatesForCheckoutAsync(checkout)).Status == Status.Processing)
                    {
                        await Task.Delay(500);
                    }
                    shippingRates = result.ShippingRates;
                }
                catch (NSErrorException ex)
                {
                    Console.WriteLine("Failed to retrieve shipping rates: {0}", ex.Error);
                }
            }
        }