Using the following wsdl: https://api.accounting.twinfield.com...sxml.asmx?wsdl

According to an example we need to set the namespace in the soap:envelope. How to do this in Dataflex?
Sending it without "xmlns:twinfield="http://www.twinfield.com/"" results in an error: "Server was unable to process request. ---> Value cannot be null.Parameter name: key"



Working from Postman:
Code:

<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" xmlns:twinfield="http://www.twinfield.com/">    
<soap:Header>
        <twinfield:Header>
            <twinfield:AccessToken>xxx</twinfield:AccessToken>
        </twinfield:Header>
    </soap:Header>
    <soap:Body>
        <twinfield:ProcessXmlDocument>
            <twinfield:xmlRequest>
                <list>
                    <type>offices</type>
                </list>
            </twinfield:xmlRequest>
        </twinfield:ProcessXmlDocument>
    </soap:Body>
</soap:Envelope>
Any thoughts how to set the psnamespace?