Push notification from C# winform application to android

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C#

Android

I have successful to register device id on gcm server from android app.
Now i want send notification from C# winform application.I am using this following code but i am getting error called
The remote server returned an error: (401) Unauthorized.

Please help me
This is my code

What I have tried:

string GoogleAppID = "AIzaSyB8vlCeU_MIiDVXFYl0uOxZNt9xZF7jHQ4";
var SENDER_ID = "851345542956";
var value = message;
WebRequest tRequest;
tRequest = WebRequest.Create("https://android.googleapis.com/gcm/send");

tRequest.Method = "post";
tRequest.ContentType = " application/x-www-form-urlencoded;charset=UTF-8";
tRequest.Headers.Add(string.Format("Authorization: key={0}", GoogleAppID));

tRequest.Headers.Add(string.Format("Sender: id={0}", SENDER_ID));
string postData = "collapse_key=score_update&time_to_live=108&delay_while_idle=1&data.message=" + value + "&data.time=" + System.DateTime.Now.ToString() + "®istration_id=" + deviceId + "";
Console.WriteLine(postData);
Byte[] byteArray = Encoding.UTF8.GetBytes(postData);
tRequest.ContentLength = byteArray.Length;

Stream dataStream = tRequest.GetRequestStream();
dataStream.Write(byteArray, 0, byteArray.Length);
dataStream.Close();


WebResponse tResponse = tRequest.GetResponse();
dataStream = tResponse.GetResponseStream();
StreamReader tReader = new StreamReader(dataStream);
String sResponseFromServer = tReader.ReadToEnd();


tReader.Close();
dataStream.Close();
tResponse.Close();
return sResponseFromServer;