Amazon-SP-API-CSharp: Order -> BuyerInfo -> BuyertaxInfo is null

maybe someone can help me.

How can i get the buyer tax informations?

Here is my code. The object is every time null:

AmazonConnection amazonConnection = new AmazonContext().GetConnection();

            ParameterOrderList serachOrderList = new ParameterOrderList();
            serachOrderList.MarketplaceIds = new List<string> { MarketPlace.Germany.ID };
            serachOrderList.AmazonOrderIds = new List<string>();
            serachOrderList.AmazonOrderIds.Add("XXXXX");
 
            var restrictedResource = new RestrictedResource();
            restrictedResource.method = Method.GET.ToString();
            restrictedResource.path = ApiUrls.OrdersApiUrls.Orders;
            restrictedResource.dataElements = new List<string> { "buyerInfo", "shippingAddress" };

            var createRDT = new CreateRestrictedDataTokenRequest()
            {
                restrictedResources = new List<RestrictedResource> { restrictedResource }
            };
            serachOrderList.RestrictedDataTokenRequest = createRDT;
            serachOrderList.IsNeedRestrictedDataToken = true;

            var orders = amazonConnection.Orders.GetOrders(serachOrderList);

Is ther a other function to get the tex informations?