EventBus comunication between activity and service

I’m working on an Android application with EventBus library. I have an activity and a service. I want to to fire an event from activity and receive it on service.

The activity is:

public class MainActivity extends AppCompatActivity {

    public static final String TAG="ACTIVITY";

    @Subscribe(threadMode = ThreadMode.MAIN)
    public void onMessageEvent(StartEvent event) {
        Log.d(TAG, "Received message");
        Snackbar.make(fab, "Stop task", Snackbar.LENGTH_LONG).show();
        txtMessage.setText(event.message);
    };

    FloatingActionButton fab;


    TextView txtMessage;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        txtMessage=findViewById(R.id.txtMessage);
        fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Start background process", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
                txtMessage.setText("Begin");
                Log.d(TAG,Thread.currentThread().getName()+ " ");
                EventBus.getDefault().post(new StartEvent());
            }
        });
    }

    @Override
    protected void onPause() {
        EventBus.getDefault().unregister(this);
        super.onPause();
    }

    @Override
    protected void onResume() {
        // registriamo un receiver per ricevere una notifica alla fine del servizio in background
        EventBus.getDefault().register(this);
        super.onResume();
    }


}

The service is:

public class MyService extends Service {
    public static final String TAG="SERVICE";

    public MyService() {
    }

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        return START_STICKY_COMPATIBILITY;
    }

    @Override
    public void onCreate() {
        super.onCreate();
        EventBus.getDefault().register(this);

    }

    @Override
    public void onDestroy() {
        EventBus.getDefault().unregister(this);
        super.onDestroy();
    }

    @Subscribe
    public void onEvent(StartEvent event){
        Log.d(TAG, "BEGIN process in background su thread "+Thread.currentThread().getName());

        try {
            Thread.sleep(10000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        Log.d(TAG, "END processo in background su thread "+Thread.currentThread().getName());

        MessageEvent message=new MessageEvent();
        message.message="Operazione in background terminata!";
        EventBus.getDefault().post(message);
    }

}

The manifest is:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.myapplication6">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity
            android:name=".MainActivity"
            android:label="@string/app_name"
            android:theme="@style/AppTheme.NoActionBar">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <service
            android:name=".MyService"
            android:enabled="true"
            android:exported="true"></service>
    </application>

</manifest>

When i press button on activity to start background task, EventBus show me the following message on logcat:

ACTIVITY: main 
EventBus: No subscribers registered for event class xx.StartEvent
EventBus: No subscribers registered for event class org.greenrobot.eventbus.NoSubscriberEvent

What is wrong?