Sales Order DI API Tax Change

Hi, Experts. I have tried to change Tax Rate on Sales Order by DI API. However, It has not worked still. I am really tired with that. Besides, It make me extremely wondering. Please help me.

SAP B1 9.0 PL06 Test

            Documents oORDR = (Documents)oCompany.GetBusinessObject(BoObjectTypes.oOrders);
       

            oORDR.CardCode = "C10011";
            oORDR.DocDate = DateTime.ParseExact("20131220", "yyyyMMdd", null);
            oORDR.DocDueDate = DateTime.ParseExact("20131220", "yyyyMMdd", null);
            oORDR.TaxDate = DateTime.ParseExact("20131220", "yyyyMMdd", null);

            oORDR.BPL_IDAssignedToInvoice = 1;

            oORDR.DocType = BoDocumentTypes.dDocument_Items;
            oORDR.Lines.ItemCode = "2109260-2";
            oORDR.Lines.Quantity = 1;
            oORDR.Lines.UnitPrice = 100;
            oORDR.Lines.VatGroup = "A8";
            oORDR.Lines.LineTotal = 100;
            oORDR.Lines.TaxTotal = 200;
            oORDR.Lines.Add();

            if (oORDR.Add() != 0)
            {
                oCompany.GetLastErrorDescription();
            }
            else
            {
            }

have tried to make Sales Order documents as shown below. It is working with UI API but it is not working with DI API.