Manage namespace in child element in XML file

Question

I am working on create XML string through Class object in C#. I am trying to add namespace in child element, but it's added in parent element of XML̥ file.

I have tried below code:

 [XmlRoot(ElementName = "Envelope", Namespace = "http://schemas.xmlsoap.org/soap/envelope/")]
    public class EnvelopeObj
    {
        [XmlElement(ElementName = "Header", Namespace = "http://schemas.xmlsoap.org/soap/envelope/")]
        public Header Header { get; set; } = new();

        [XmlElement(ElementName = "Body", Namespace = "http://schemas.xmlsoap.org/soap/envelope/")]
        public Body Body { get; set; } = new();       
    }

    public class Header { }


    public class Body
    {
        [XmlElement(ElementName = "StoreOrderRequest", Namespace = "http://test.com/wsdl/OrderingMobility/v8_0")]
        public StoreOrderRequestMain StoreOrderRequest { get; set; } = new();
      
    }

    [XmlRoot(ElementName = "StoreOrderRequest", Namespace = "http://test.com/wsdl/OrderingMobility/v8_0")]
    public class StoreOrderRequestMain
    {
        [XmlElement(ElementName = "MessageHeader", Namespace = "http://test.com/schema/MsgHeader/v1_0")]
        public MessageHeader MessageHeader { get; set; } = new();

        [XmlElement(ElementName = "StoreOrderRequest", Namespace = "")]
        public StoreOrderRequestObj StoreOrderRequest { get; set; } = new();
       
    }

    public class StoreOrderRequestObj
    {
        public string AccountGroupId { get; set; }
       
    }

 [XmlRoot(ElementName = "MessageHeader", Namespace = "http:/test.com/schema/MsgHeader/v1_0")]
    public class MessageHeader
    {
        public string AgreementId { get; set; }        
    }

Please look in below code to convert xml string:

EnvelopeObj envelope = new ();


                XmlSerializerNamespaces namespaces = new XmlSerializerNamespaces();
                namespaces.Add("", "http://test.att.com/schema/OrderingMobility/v8_0");
                namespaces.Add("SOAPENC", "http://schemas.xmlsoap.org/soap/encoding/");
                namespaces.Add("xsd", "http://www.w3.org/2001/XMLSchema");
                namespaces.Add("xsi", "http://www.w3.org/2001/XMLSchema-instance");
                namespaces.Add("SOAP-ENV", "http://schemas.xmlsoap.org/soap/envelope/");
                namespaces.Add("m", "http://test.com/wsdl/OrderingMobility/v8_0");

                // Create an XmlSerializer for the MyClass type
                XmlSerializer serializer = new XmlSerializer(typeof(EnvelopeObj));

                Encoding encoding = Encoding.UTF8;
                string xmlString = string.Empty;
                using (MemoryStream memoryStream = new MemoryStream())
                {
                    // Create an XmlWriter with the specified encoding
                    using (XmlWriter xmlWriter = XmlWriter.Create(memoryStream, new XmlWriterSettings { Encoding = encoding,Indent=true, OmitXmlDeclaration = true }))
                    {
                        // Serialize the object
                        serializer.Serialize(xmlWriter, envelope,namespaces);
                    }

                    // Convert the MemoryStream to a byte array
                    byte[] xmlBytes = memoryStream.ToArray();

                    // Convert the byte array to a string using the specified encoding
                     xmlString = encoding.GetString(xmlBytes);

                    // Print the XML string
                    Console.WriteLine(xmlString);
                }

With above code I am getting below XML string:

<?xml version="1.0" encoding="utf-8"?>
<SOAP-ENV:Envelope
    xmlns="http://test.com/schema/OrderingMobility/v8_0"
    xmlns:xsd="http://www.w3.org/2001/XMLSchema"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:SOAPENC="http://schemas.xmlsoap.org/soap/encoding/"
    xmlns:m="http://test.com/wsdl/OrderingMobility/v8_0"
    xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/">
    <SOAP-ENV:Header />
    <SOAP-ENV:Body>
        <m:StoreOrderRequest>
            <MessageHeader xmlns="http://test.com/schema/MsgHeader/v1_0">
                
                <AgreementId>987456123</AgreementId>
                
            </MessageHeader>
            <StoreOrderRequest xmlns="">
                <AccountGroupId>123456789</AccountGroupId>              
            </StoreOrderRequest>
        </m:StoreOrderRequest>
    </SOAP-ENV:Body>
</SOAP-ENV:Envelope>

But I want below result Can anyone please guide me what mistakes I have done in code.

<?xml version="1.0" encoding="UTF-8"?>
<SOAP-ENV:Envelope
    xmlns="http://test.com/schema/OrderingMobility/v8_0"
    xmlns:SOAPENC="http://schemas.xmlsoap.org/soap/encoding/"
    xmlns:xsd="http://www.w3.org/2001/XMLSchema"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/">
    <SOAP-ENV:Header />
    <SOAP-ENV:Body>
        <m:StoreOrderRequest xmlns:m="http://test.com/wsdl/OrderingMobility/v8_0">
            <MessageHeader xmlns="http://test.com/schema/MsgHeader/v1_0">
                <AgreementId>987654321</AgreementId>                
            </MessageHeader>
            <StoreOrderRequest>
                <AccountGroupId>123456789</AccountGroupId>              
            </StoreOrderRequest>
        </m:StoreOrderRequest>
    </SOAP-ENV:Body>
</SOAP-ENV:Envelope>