public class MessagingService extends FirebaseMessagingService {

    public static String TAG = MessagingService.class.getSimpleName();

    @Override
    public void onNewToken(String s) {
        super.onNewToken(s);
        Log.e(TAG,"NEW TOKEN IS: "+s);
    }

    @Override
    public void onMessageReceived(RemoteMessage remoteMessage) {
        super.onMessageReceived(remoteMessage);
        Log.e(TAG,"NEW MESSAGE RECEIVED FROM SERVER!");
    }
}

<application
.....

<activity>
......
</activity>

<meta-data
            android:name="com.google.android.geo.API_KEY"
            android:value="@string/google_maps_key" />
        <meta-data
            android:name="com.google.android.gms.version"
            android:value="@integer/google_play_services_version" />

        <meta-data
            android:name="com.google.firebase.messaging.default_notification_channel_id"
            android:value="fcm_default_channel" />

<service android:name="ats.it.vn.furgodemo.util.notification.MessagingService">
            <intent-filter>
                <action android:name="com.google.firebase.MESSAGING_EVENT" />
            </intent-filter>
        </service>

</application>