How to sync my customer data to quickbooks through web connector? - web-services

Question

I have Quickbooks Desktop Enterprise 18.0. I already created connection using qwc file through web connector.when I click Update selected option from web connector the result says okay. But If I include customer data in web service and click Update selected it shows error in status bar i.e Description:
Error message received from application via getLastError(): Error!.
I pasted code below Please review it and Guide if there anything wrong. Thank you.
public ArrayList buildRequest() {
string strRequestXML ="";
XmlDocument inputXMLDoc = null;
// CustomerQuery
inputXMLDoc = new XmlDocument();
inputXMLDoc.AppendChild(inputXMLDoc.CreateXmlDeclaration("1.0",null, null));
inputXMLDoc.AppendChild(inputXMLDoc.CreateProcessingInstruction("qbxml", "version=\"4.0\""));
XmlElement qbXML = inputXMLDoc.CreateElement("QBXML");
inputXMLDoc.AppendChild(qbXML);
XmlElement qbXMLMsgsRq = inputXMLDoc.CreateElement("QBXMLMsgsRq");
qbXML.AppendChild(qbXMLMsgsRq);
qbXMLMsgsRq.SetAttribute("onError", "stopOnError");
XmlElement CustomerAddRq = inputXMLDoc.CreateElement("CustomerAddRq");
qbXML.AppendChild(CustomerAddRq);
qbXMLMsgsRq.SetAttribute("requestID", "1");
XmlElement CustomerAdd = inputXMLDoc.CreateElement("CustomerAdd");
CustomerAddRq.AppendChild(CustomerAdd);
XmlElement Name = inputXMLDoc.CreateElement("Name");
CustomerAdd.AppendChild(Name);
CustomerAdd.AppendChild(Name).InnerText = "Naga";
XmlElement FirstName = inputXMLDoc.CreateElement("FirstName");
CustomerAdd.AppendChild(FirstName);
CustomerAdd.AppendChild(Name).InnerText = "Nagarajan";
XmlElement MiddleName = inputXMLDoc.CreateElement("MiddleName");
CustomerAdd.AppendChild(MiddleName);
XmlElement LastName = inputXMLDoc.CreateElement("LastName");
CustomerAdd.AppendChild(LastName);
CustomerAdd.AppendChild(Name).InnerText = "Varatharajan";
XmlElement BillAddress = inputXMLDoc.CreateElement("BillAddress");
CustomerAdd.AppendChild(BillAddress);
XmlElement Addr1 = inputXMLDoc.CreateElement("Addr1");
BillAddress.AppendChild(Addr1);
BillAddress.AppendChild(Addr1).InnerText = "33/33 st";
XmlElement City = inputXMLDoc.CreateElement("City");
BillAddress.AppendChild(City);
BillAddress.AppendChild(City).InnerText = "Chennai";
XmlElement State = inputXMLDoc.CreateElement("State");
BillAddress.AppendChild(State);
BillAddress.AppendChild(State).InnerText = "TN";
XmlElement Phone = inputXMLDoc.CreateElement("Phone");
CustomerAdd.AppendChild(Phone);
CustomerAdd.AppendChild(Phone).InnerText = "4545455";
//XmlElement customerQueryRq = inputXMLDoc.CreateElement("CustomerQueryRq");
//qbXMLMsgsRq.AppendChild(customerQueryRq);
//customerQueryRq.SetAttribute("requestID", "1");
// XmlElement maxReturned=inputXMLDoc.CreateElement("MaxReturned");
// customerQueryRq.AppendChild(maxReturned).InnerText="1";
strRequestXML = inputXMLDoc.OuterXml;
req.Add(strRequestXML);
}