Issue while integrating PayU in windows universal apps - windows

Question

I am new to Windows universal apps development. Now I am developing an app in which I have to integrate PayU. I tried a lot but everytime the transaction error is thrown from the server.
string temp1 = "key=xxxxxx&txnid=xxxxxx&hash=hashValue&amount=xxx&firstname=abc" +
"&email=a#a.com&phone=80xxxxxxxx&productinfo=xxxxxxxxxxxx" +
"&surl=https://www.google.com&furl=https://www.twitter.com" +
"&udf1=a&udf2=b&udf3=c&udf4=d&udf5=e&pg=CC&bankcode=CC" +
"&ccardtype=CC&ccnum=1234xxxxxxxxx&ccname=xxx&ccvv=xxx" +
"&ccexpmon=xx&ccexpyr=xxxx";
var httpClient = new Windows.Web.Http.HttpClient();
Windows.Web.Http.HttpRequestMessage httpRequestMessage = new Windows.Web.Http.HttpRequestMessage(Windows.Web.Http.HttpMethod.Post, theUri);
Windows.Web.Http.IHttpContent content = new Windows.Web.Http.HttpStringContent(temp1, Windows.Storage.Streams.UnicodeEncoding.Utf8);
httpRequestMessage.Content = content;
try
{
webView.NavigateWithHttpRequestMessage(httpRequestMessage);
}
catch(Exception f)
{
new MessageDialog(f.ToString()).ShowAsync();
}
And I am creating the hashValue by using method :
public String SampleHashMsg(String strMsg)
{
// Convert the message string to binary data.
string strAlgName = HashAlgorithmNames.Sha512;
IBuffer buffUtf8Msg = CryptographicBuffer.ConvertStringToBinary(strMsg, BinaryStringEncoding.Utf8);
// Create a HashAlgorithmProvider object.
HashAlgorithmProvider objAlgProv = HashAlgorithmProvider.OpenAlgorithm(strAlgName);
// Demonstrate how to retrieve the name of the hashing algorithm.
String strAlgNameUsed = objAlgProv.AlgorithmName;
// Hash the message.
IBuffer buffHash = objAlgProv.HashData(buffUtf8Msg);
// Verify that the hash length equals the length specified for the algorithm.
if (buffHash.Length != objAlgProv.HashLength)
{
throw new Exception("There was an error creating the hash");
}
// Convert the hash to a string (for display).
//String strHashBase64 = CryptographicBuffer.EncodeToBase64String(buffHash);
String strHashBase64 = CryptographicBuffer.EncodeToHexString(buffHash);
// Return the encoded string
return strHashBase64;
}
I should load the request to the webview. But I am getting an error "Transaction Error" in that.
I am getting transaction error, txnid is not provided. Well at PayU side the sent hash key will be used for verify a transaction. May be my txnid and the txnid contained by hash does not match and payu server denies the transaction saying that provide txnid.
I am using Microsoft Visual Studio 2013 Universal apps for the app development.
But still I am not getting correct result. Please if anyone can help me out, then please reply immediately. Thanks in advance.