Notifications Sending between two devices

//First you need to add a OkhttpCliente dependency on your App Gradle File.
//You can find them in the next URL: https://github.com/square/okhttp


private void sendNotification(String regToken) {
        final String regToken2 = regToken;
        final String LEGACY_SERVER_KEY = "AIzaSyD6QliPCOBwISMu35_r_MzxSY6uc0gLd7s";
        final MediaType JSON
                = MediaType.parse("application/json; charset=utf-8");

            new AsyncTask<Void,Void,Void>(){
                @Override
                protected Void doInBackground(Void... params) {
                    try {
                        OkHttpClient client = new OkHttpClient();
                        JSONObject json=new JSONObject();
                        JSONObject dataJson=new JSONObject();
                        dataJson.put("body","Hi this is sent from device to device");
                        dataJson.put("title","dummy title");
                        dataJson.put("sound", "/uri/audio/listen.mp3");
                        json.put("notification",dataJson);

                        json.put("to",regToken2);
                        RequestBody body = RequestBody.create(JSON, json.toString());
                        Request request = new Request.Builder()
                                .header("Authorization","key="+ LEGACY_SERVER_KEY)
                                .url("https://fcm.googleapis.com/fcm/send")
                                .post(body)
                                .build();
                        Response response = client.newCall(request).execute();
                        String finalResponse = response.body().string();
                    }catch (Exception e){
                        //Log.d(TAG,e+"");
                    }
                    return null;
                }
            }.execute();



    }