Error with trying to insert ItemInvoice Lines

I am getting the following error "A request should not contain UID during POST operation"

This is after I created an Item Invoice Header and then try and add Item Lines to the Invoice Header. This has worked for over 3 years. After I got the error I updated all the NuGet packages etc and still get the error. It is written in c# 4.5. Here is the code cut-down version of the code

ItemInvoice invoice = new ItemInvoice();
List<ItemInvoiceLine> lines = new List<ItemInvoiceLine>();
CustomerLink customer = new CustomerLink();
customer.UID = customerUID;
invoice.Customer = customer;
invoice.Date = Date;
invoice.IsTaxInclusive = false;
invoice.CustomerPurchaseOrderNumber =  PurchaseOrder ;
invoice.InvoiceDeliveryStatus = DocumentAction.Email;

// Create Invoice Header 

invoice =   ws.insertItemInvoice(invoice);


// Add Invoice Lines to Invoice

foreach (var orderline in orderLines)
       {
		ItemInvoiceLine line = new  ItemInvoiceLine();
            ItemLink item = new ItemLink();
            item.UID = orderline.ItemUID;
            line.Item = item;
            line.Description= orderline.Description;
            line.ShipQuantity = (decimal)orderline.Quantity;
            line.UnitPrice = (decimal)orderline.SellingPrice;
            TaxCodeLink taxCode = new TaxCodeLink();
            taxCode.UID = TaxUID;
            line.TaxCode = taxCode;
            lines.Add(line);
            orderline.SaleUID = invoice.UID; 
            invoice.Lines = lines; 
		var itemInvoiceSvc = new ItemInvoiceService(_configurationCloud, null, _oAuthKeyService);
		itemInvoiceSvc.InsertEx(companyFile, invoice, credentials);
	}