Sample code in C# to list an Item with mixed shipping types using .NET SDK

public string AddItem(string UUID)
{
AddItemCall addItem = new AddItemCall(GetContext());
ItemType item = new ItemType();
item.Currency = CurrencyCodeType.USD;
item.Country = CountryCodeType.US;

item.Title = 'title';
item.Quantity = 1;
item.PostalCode = '95125';
item.ListingDuration = 'Days_7';
item.PrimaryCategory = new CategoryType();
item.PrimaryCategory.CategoryID = '146301';
item.StartPrice = new AmountType();
item.StartPrice.currencyID = CurrencyCodeType.USD;
item.StartPrice.Value = 20;
item.UUID = UUID;

item.ShippingDetails = new ShippingDetailsType();
// Flat Domestic Calculated International Shipping Type
item.ShippingDetails.ShippingType = ShippingTypeCodeType.FlatDomesticCalculatedInternational;

// Domestic Shipping Services
item.ShippingDetails.ShippingServiceOptions = new ShippingServiceOptionsTypeCollection();
ShippingServiceOptionsType[] opt = new ShippingServiceOptionsType[1];
opt[0] = new ShippingServiceOptionsType();
opt[0].ShippingServiceCost = new AmountType();
opt[0].ShippingServiceCost.currencyID = CurrencyCodeType.USD;
opt[0].ShippingServiceCost.Value = 5;
opt[0].ShippingService = 'USPSPriority';
opt[0].ShippingServicePriority = 1;
item.ShippingDetails.ShippingServiceOptions.Add(opt[0]);

// Calculated Shipping values
CalculatedShippingRateType calRate = new CalculatedShippingRateType();
calRate.OriginatingPostalCode = '95125';
calRate.ShippingPackage = ShippingPackageCodeType.PackageThickEnvelope;
calRate.WeightMajor = new MeasureType();
calRate.WeightMajor.unit = 'lbs';
calRate.WeightMajor.Value = 2;
calRate.WeightMinor = new MeasureType();
calRate.WeightMinor.unit = 'oz';
calRate.WeightMinor.Value = 6;
item.ShippingDetails.CalculatedShippingRate = calRate;

// International Shipping Services
item.ShippingDetails.InternationalShippingServiceOption = new InternationalShippingServiceOptionsTypeCollection();
InternationalShippingServiceOptionsType[] Iopt = new InternationalShippingServiceOptionsType[1];
Iopt[0] = new InternationalShippingServiceOptionsType();
Iopt[0].ShippingService = 'USPSGlobalExpress';
Iopt[0].ShippingServicePriority = 1;
item.ShippingDetails.InternationalShippingServiceOption.Add(Iopt[0]);
Iopt[0].ShipToLocation = new StringCollection();
Iopt[0].ShipToLocation.Add('Worldwide');

FeeTypeCollection fees = addItem.AddItem(item);
return item.ItemID;
}

// Credentials for the call
context.ApiCredential.eBayToken = 'token';

// Set the URL
context.SoapApiServerUrl = 'https://api.sandbox.ebay.com/wsapi';

// Set logging
context.ApiLogManager = newApiLogManager();
context.ApiLogManager.ApiLoggerList.Add(new eBay.Service.Util.FileLogger('Messages.log', true, true, true));
context.ApiLogManager.EnableLogging = true;

// Set the version
context.Version = '1131';

return context;