What does "posting well formed XML" mean?

I have a vendor provided WSDL. I'm trying to call their methods but can't get the code working. I can use a Soap emulator and call their WSDl XML. I emailed the vendor and that is what they wrote:

In the general case, yes, you will need to post well formed XML content to the API, but whether you do that manually or via some stub generator is up to you.

Not sure what that means. This is one example of their XML:

<soap:Envelope xmlns:soap="http://www.w3.org/2003/05/soap-envelope" xmlns:xsd="http://www.test.com/IpsApi/xsd" xmlns:ns="http://www.test.com/IpsApi/xsd/2010-01-31">
   <soap:Header>
      <xsd:authHeader>
         <xsd:user>test@test.com</xsd:user>
         <xsd:password>test</xsd:password>
      </xsd:authHeader>
   </soap:Header>
   <soap:Body>
      <ns:checkLoginParam>

         <ns:email>test@test.com</ns:email>
         <ns:password>test</ns:password>
      </ns:checkLoginParam>
   </soap:Body>
</soap:Envelope>

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