title: firebase (fcm) says 401 unauthorized
body: <pre><code>private void sendMsg() {
      DBManager dbManager = DBManager.getInstance();
      ArrayList&lt;String&gt; firebaseIds;
  
      try {
          ResultSet rs= dbManager.getRegisteredFirebaseDevice();
          while(rs.next()){
              System.out.println(rs.getString(1));
              firebaseIds.add(rs.getString(1));
          }
      } catch (SQLException e) {
          e.printStackTrace();
      }
  
      String url = "https://fcm.googleapis.com/fcm/send";
      URL obj = new URL(url);
      HttpURLConnection con = (HttpURLConnection) obj.openConnection();
  
      // add reuqest header
      con.setRequestMethod("POST");
      con.setRequestProperty("Authorization: key", "AIzaSyAl6S936qt_NKKFwwbd-NEmiSGIL7G_yJc");
      con.setRequestProperty("Content-Type", "application/json");
      // String msg="New design added in "+getCategory(designCategory)+". Design no."+designNo;
      // String urlParameters = "data.msg="+msg+"&amp;registration_id="+firebaseIds.get(0);
  
      JSONObject msg=new JSONObject();
      msg.put("msg","New design added in "+getCategory(designCategory)+". Design no."+designNo);
  
  
      JSONObject parent=new JSONObject();
  
      parent.put("to", firebaseIds.get(0));
      parent.put("data", msg);
  
      // String urlParameters = "registration_id="+firebaseIds.get(0);
      // Send post request
      con.setDoOutput(true);
  
  
      OutputStreamWriter wr= new OutputStreamWriter(con.getOutputStream());
      wr.write(parent.toString());
  
      // DataOutputStream wr = new DataOutputStream(con.getOutputStream());
      // wr.writeBytes(urlParameters);
      // wr.flush();
      // wr.close();
  
      int responseCode = con.getResponseCode();
      System.out.println("\nSending 'POST' request to URL : " + url);
      System.out.println("Post parameters : " + parent.toString());
      System.out.println("Response Code : " + responseCode+" "+con.getResponseMessage());
  
  }
  </code></pre>
  
  <p>When I call the above code, it gives me response as <code>401 Unauthorized</code>. I am not able to understand why I am getting this error. I have used proper server key. Is there any syntax error or anything wrong in the strategy used by me. </p>
  
  <p>I have followed the <a href="https://firebase.google.com/docs/cloud-messaging/server#implementing-http-connection-server-protocol" rel="noreferrer">https://firebase.google.com/docs/cloud-messaging/server#implementing-http-connection-server-protocol</a> documentation</p>