Prefix in Xml developing with c#

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C#

XML

Hi everyone.

I have a problem developing code with xml and c#. I am trying to create the following Xml code:

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ws="http://ws.eurosur.gmv.com/">
   <soapenv:Header/>
   <soapenv:Body>
     xxxxxxxxxxxxxxx
   </soapenv:Body>

I am trying to create it, with the following code

String sXml = @"<?xml version='1.0' encoding='utf-8'?> " +
"<soapenv:Envelope xmlns:soapenv=\"http://schemas.xmlsoap.org/soap/envelope/\" xmlns:ws=\"http://ws.dfdf.com/\"/>";
                
oXmlDocument.LoadXml(sXml);
XmlNamespaceManager omanager = new XmlNamespaceManager(oXmlDocument.NameTable);
omanager.AddNamespace("env", "http://schemas.xmlsoap.org/soap/envelope/");
omanager.AddNamespace("ns2", "http://ws.dfdf.com/");
omanager.AddNamespace("soapenv", "http://schemas.xmlsoap.org/soap/envelope/");
omanager.AddNamespace("ws", "http://ws.eurosur.gmv.com/");
                
XMLUtils oXMLUtils = new XMLUtils(oXmlDocument);
XmlNode oXmlBody = oXMLUtils.createNodeElement("soapenv:Body", "");
                oXMLUtils.insertAfter(oXmlDocument.SelectSingleNode("soapenv:Envelope", omanager), oXmlBody, null);

XmlNode oXmlCreate = oXMLUtils.createNodeElement("ws:updateArtefact", "");
                oXMLUtils.insertAfter(oXmlDocument.SelectSingleNode("soapenv:Envelope/Body", omanager), oXmlCreate, null);

XmlNode oXmlHeader = oXMLUtils.createNodeElement("soapenv:Header", "");
                oXMLUtils.insertAfter(oXmlDocument.SelectSingleNode("soapenv:Envelope", omanager), oXmlHeader, null);

return oXmlDocument;

But when I view the result, the prefix of the tags doesn´t appear.

But in the properties of the xmlnode it is assigned.

Can someone tell me what I am doing wrong??

Thank you very much