Send FCM Notifications in C#

public string SendNotificationJSON(string deviceId, string title, string body, string click_action)
{
    string SERVER_KEY_TOKEN = "SERVER_KEY_TOKEN";
    var SENDER_ID = "SENDER_ID";
 
    WebRequest tRequest;
    tRequest = WebRequest.Create("https://fcm.googleapis.com/fcm/send");
    tRequest.Method = "post";
    tRequest.ContentType = " application/json";
 
    tRequest.Headers.Add(string.Format("Authorization: key={0}", SERVER_KEY_TOKEN));
    tRequest.Headers.Add(string.Format("Sender: id={0}", SENDER_ID));
 
    var a = new
    {
        notification = new 
        {
            title,
            body,
            icon = "https://domain/path/to/logo.png",
            click_action,
            sound = "mySound"
        },
        to = deviceId
    };
 
    byte[] byteArray = Encoding.UTF8.GetBytes(Newtonsoft.Json.JsonConvert.SerializeObject(a));
    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;
}