I am new in Android development and I am trying to work on a project which involves an application that uses Firebase database. I want to send notifications to users when something happens, i.e. when I assign a task to a user.
I have implemented necessary Firebase classes and I can successfully send notifications to users, using their token from Firebase console. However, I can't manage to send custom notifications from the code in Android Studio.
I have tried the following function and I am passing the token of a device plus a title and a body for the notification and it's not working.
public static void pushFCMNotification(String userDeviceIdKey, String title, String body) throws     Exception{
    String authKey = AUTH_KEY_FCM;   // You FCM AUTH key
    String FMCurl = API_URL_FCM;
    URL url = new URL(FMCurl);
    HttpURLConnection conn = (HttpURLConnection) url.openConnection();
    conn.setUseCaches(false);
    conn.setDoInput(true);
    conn.setDoOutput(true);
    conn.setRequestMethod("POST");
    conn.setRequestProperty("Authorization","key="+authKey);
    conn.setRequestProperty("Content-Type","application/json");
    JSONObject json = new JSONObject();
    json.put("to",userDeviceIdKey);
    JSONObject info = new JSONObject();
    info.put("title", title);   // Notification title
    info.put("body", body); // Notification body
    json.put("notification", info);
    OutputStreamWriter wr = new OutputStreamWriter(conn.getOutputStream());
    wr.write(json.toString());
    wr.flush();
    conn.getInputStream();
}
Can someone give me some guidelines or any other ways of implementing such notifications?