http post in c# - the data isn't submitted right or not at all

See more:

HTTP

XSS

scan

I am trying to create an xss scanner for a project. I have written the code below in order to send http post with xss payload to see if the website I'm checking is vulnerable to xss. I have a learning xss site - which is certainly vulnerable to xss to check my code on. What I'm supposed to see in the response is my xss payload in the site's input vector. My problem is that the postData (AKA my xss payload) is not submitted right to the site or even not submitted at all. What can I do so the postData will be submitted (correctly) in order to recognize the attack/vulnerability later on? Thank you very much!!

string line;
var postData = "";

ServicePointManager.UseNagleAlgorithm = true;
ServicePointManager.Expect100Continue = true;
ServicePointManager.CheckCertificateRevocationList = true;
ServicePointManager.DefaultConnectionLimit = ServicePointManager.DefaultPersistentConnectionLimit;

//openning a writing stream to the output file
StreamWriter xssOptionalfile = new StreamWriter(pathFile);

//read the xxs payloads file and display it line by line.
StreamReader file = new StreamReader("D:/USER/Desktop/xssStrings.txt");
string specificPayloadInputNames = "";
int countXss = 1;//will count our xss payloads
string possibleXssPayload = "";//will store the xss payloads that worked
//goes over all the xss payloads we have stored in a file, inserts them into the input vector
//and checks what happens
file.BaseStream.Position = 0;//return StreamReader to the beginning

while ((line = file.ReadLine()) != null)
{
    specificPayloadInputNames = "";

    //creates the request
    WebRequest request = WebRequest.Create(URLaddress);
    //set the Method property of the request to POST.
    request.Method = "POST";
    specificPayloadInputNames = "";
    //goes over all the input vectors inorder to insert the xss payload to each one of them
    for (int i = 0; i < elements.Count; i++)
    {
        //Create POST data
        if (elements[i].Name.ToString() != "")
            postData = elements[i].Name.ToString() + "=" + line;
        else
            postData = "";
        for (int j = 0; j < elements.Count; j++)//
            if (j != i && elements[j].Name.ToString()!="")
            {
                postData += ("&" + elements[j].Name.ToString() + "=" + "try");
            }

        //convert the POST data to a byte array
        byte[] byteArray = Encoding.UTF8.GetBytes(postData);
        //set the ContentType property of the WebRequest
       request.ContentType = "text/xml; encoding='utf-8'";
        //set the ContentLength property of the WebRequest
        request.ContentLength = byteArray.Length;
        //get the request stream
        Stream dataStream = request.GetRequestStream();
        //write the data to the request stream
        dataStream.Write(byteArray, 0, byteArray.Length);
        //close the Stream object
        dataStream.Close();
        //get the response
        WebResponse response = request.GetResponse();
        //get the stream containing content returned by the server
        dataStream = response.GetResponseStream();

        //open the stream using a StreamReader for easy access
        StreamReader reader = new StreamReader(dataStream);
        //read the content
        string responseFromServer = reader.ReadToEnd();