Troubles sending XML with HTTP

Hi everyone,

I'm finding a lot of troubles develping a system for connecting our customers NAv 2013 with a courier company.
The first goal is to send an XMl file to the sercice, and get back another XML with the answer. I genrate the XML correctly, but when I start the development, I can see the next error:



"Cannot create the object...."

This is how I create the connection.

HttpWebRequest := WebRequest.Create(Uri.Uri('https://XXXXXXXXXXXXX/shipping/ship'));
HttpWebRequest.Method := 'POST';
HttpWebRequest.ContentType := 'application/xml';   
HttpWebRequest.Timeout := 120000;     
HttpWebRequest.UseDefaultCredentials(FALSE);  
XMLDocDotNet := XMLDocDotNet.XmlDocument;
XMLDoc.save('C:\XML\convert\try.xml');
XMLDocDotNet.Load('C:\XML\convert\try.xml');

ByteArray := Encoding.UTF8.GetBytes('"xml_in=' + XMLDocDotNet.OuterXml + '"');

longitud := ByteArray.Length;
HttpWebRequest.ContentLength := ByteArray.Length;


IF NOT TryCreateRequestStream(HttpWebRequest,RequestStream) THEN BEGIN
    MESSAGE('Error al crear el request Stream');
  EXIT;
END;

RequestStream.Write(ByteArray,0,ByteArray.Length);  
TryGetWebResponse(HttpWebRequest,HttpWebResponse);     
StatusCode := HttpWebResponse.StatusCode;
StatusDescription := HttpWebResponse.StatusDescription;
ResponseText := ReadHttpResponseAsText(HttpWebResponse);
lPackingHeader.ProcessResponse(ResponseText,PackingNo);

Trying different things, and having other issues with different objects, I realizes that the problem creating the node, could be because the received answer from the server is an error, so the received XML isn't as expected. S when I try to process the XML, I found the error.

So I decided to execute with the debugger, and I found this strange things:




As you can see, the RequestSteam and the ByteArray are not initialized. The byteArray is what I send in the HTTPRequest, so I think that the error may have something to do with this. Am I right?
I have to say, that I am using as example to follow the development for the "Electronic VAT Information under SII".

Thank you all for your help, I'm quite lost, so any help will be really welcome