Add product to Invoice (Write In Product)

invoicedetail objDetails = new invoicedetail();
CrmBoolean objProductOverride = new CrmBoolean();
objProductOverride.Value = true;//
objDetails.isproductoverridden = objProductOverride;
productName = ConfigurationSettings.AppSettings["ProductLineItem_Prefix"].ToString() + " - " + dt_kidsSupported.Rows[kd]["KidName"].ToString();
objDetails.productdescription = productName;
CrmDecimal objDec = new CrmDecimal();
objDec.Value = Convert.ToDecimal("1", CultureInfo.InvariantCulture);
objDetails.quantity = objDec;
CrmMoney objDec1 = new CrmMoney();
objDec1.Value = SponsordAmount;
objDetails.priceperunit = objDec1;
objDetails.invoiceid = new Lookup();
objDetails.invoiceid.Value = invoiceId;
objDetails.invoiceid.type = EntityName.invoice.ToString();
service.Create(objDetails);