in Android, Periodic work only runs one time and stops after quitting the app

Question

I created a sample Android application to send requests every 12 hours, I used worker class to achieve this, and I implemented like below, for testing purposes I have changed the time to 6 Sec, but it's not changing every 6 seconds, what went wrong here, Thanks in Advance

MyWorker.class

public class MyWorker extends Worker {
    private static final String TAG = "MyWorker";
    public MyWorker(@NonNull Context context, @NonNull WorkerParameters params) {
        super(context, params);
    }

    @NonNull
    @Override
    public Result doWork() {
        Log.d(TAG, "doWork: now.... doing it");
        sendRequest();
        // Do your background work here
        // This is where you'll put the code you want to run periodically
        return Result.success(); // Indicate success
    }

    private void sendRequest() {
        //send
    }
}

in the MainActivity.class inside the onCreate method

   private void doWork() {
//        Constraints constraints = new Constraints.Builder()
//                .setRequiredNetworkType(NetworkType.CONNECTED)
//                .build();

        Constraints constraints = new Constraints.Builder()
                .setRequiredNetworkType(NetworkType.UNMETERED) // This allows work to run on unmetered networks (Wi-Fi)
                .build();

//        PeriodicWorkRequest periodicWorkRequest =
//                new PeriodicWorkRequest.Builder(MyWorker.class, 12, TimeUnit.HOURS)
//                        .setConstraints(constraints)
//                        .build();

        PeriodicWorkRequest periodicWorkRequest =
                new PeriodicWorkRequest.Builder(MyWorker.class, 6, TimeUnit.SECONDS)
                        .setConstraints(constraints)
                        .build();

        WorkManager.getInstance(this).enqueue(periodicWorkRequest);
    }

Manifest inside the application tag

           <service
            android:name=".MyWorker"
            android:exported="false"
            android:permission="android.permission.BIND_JOB_SERVICE" />

Thanks in Advance,