Working easily with FCM push notifications in Android ,

Send Notification Firbase Android Java

    final private String FCM_API = "https://fcm.googleapis.com/fcm/send";
    //server Key => get From Your Firbase account 
    final private String serverKey = "key=" + "AAAA.......";
    final private String contentType = "application/json";
    final String TAG = "NOTIFICATION TAG";

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newMessageDoc.set(newChatMessage).addOnCompleteListener(task -> {
            if (task.isSuccessful()) {
            // topic when user login , using this code in the response 
            //FirebaseMessaging.getInstance().subscribeToTopic("user_" + user.getId());
            
                TOPIC = "/topics/user_" + userRecever.getId(); //topic has to match what the receiver subscribed to
                NOTIFICATION_TITLE = "Ahmed M Bader El-Din"; // title notification 
                // in this example title my name 
                NOTIFICATION_MESSAGE = "Hi How Are You!!!";

                JSONObject notification = new JSONObject();
                JSONObject notifcationBody = new JSONObject();
                try {
                    notifcationBody.put("title", NOTIFICATION_TITLE);
                    notifcationBody.put("chatID", id_chat);// using this becuse when the user revice message , when click notify can you open the chat directly (^_^)
                    notifcationBody.put("body", NOTIFICATION_MESSAGE);
                    Log.i("sendMessage", "sendMessage: " + TOPIC + " " + notifcationBody);
                    notification.put("to", TOPIC);//send this notifi to user_topic // e.g user_1234
                    notification.put("notification", notifcationBody); // notification
                    notification.put("data", notifcationBody);//data for notification
                } catch (JSONException e) {
                    Log.e(TAG, "onCreate: " + e.getMessage());
                }
                sendNotification(notification);
            } else {
                View parentLayout = findViewById(android.R.id.content);
                Snackbar.make(parentLayout, "Something went wrong.", Snackbar.LENGTH_SHORT).show();
            }
        });

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private void sendNotification(JSONObject notification) {
//FCM_API => URL 
        JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(FCM_API, notification,
                response -> {
                    Log.i("onResponse", "onResponse: " + response.toString());
                },
                error -> {
                    Toast.makeText(MessageActivity.this, "Request error", Toast.LENGTH_LONG).show();
                    Log.i("onErrorResponse", "onErrorResponse: Didn't work");
                }) {
            @Override
            public Map<String, String> getHeaders() {
                Map<String, String> params = new HashMap<>();
                params.put("Authorization", serverKey);
                params.put("Content-Type", contentType);
                return params;
            }
        };
        VolleySingleton.getInstance(getApplicationContext()).addToRequestQueue(jsonObjectRequest);
    }