title: FCM (Firebase Cloud Messaging) Send to multiple devices
body: <p>I execute this code to push notifications to mobile device using FCM library</p>
  
  <pre><code>public string PushFCMNotification(string deviceId, string message) 
      {
          string SERVER_API_KEY = "xxxxxxxxxxxxxxxxxxxxxxx";
          var SENDER_ID = "xxxxxxxxx";
          var value = message;
          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_API_KEY));
  
          tRequest.Headers.Add(string.Format("Sender: id={0}", SENDER_ID));
  
          var data = new
          {
              to = deviceId,
              notification = new
              {
                  body = "This is the message",
                  title = "This is the title",
                  icon = "myicon"
              }
          };
  
          var serializer = new JavaScriptSerializer();
          var json = serializer.Serialize(data);
  
          Byte[] byteArray = Encoding.UTF8.GetBytes(json);
  
          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;
      }
  </code></pre>
  
  <p>now, how to send message to multi device,
  assume that string deviceId parameter replaced with List devicesIDs.</p>
  
  <p>can you help</p>