Check if the android:showOnLockScreen, android:showWhenLocked, and android:turnScreenOn parameters are set to "true" in your AndroidManifest.xml?

I want to open an activity when a push notification is received from FCM to my Android Oreo. But it’s not working. I have tried adding an HTTP call in onMessageReceived method and that works as expected. But it will not start an activity, as in the code below:

@Override
public void onMessageReceived(@NonNull RemoteMessage remoteMessage) {
    super.onMessageReceived(remoteMessage);

    //http call which succeeds

    Intent intent = new Intent(this, MainActivity.class);
    intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
    startActivity(intent);
}

The manifest has this service definition:

    <service
        android_name=".services.CheckerService"
        android_exported="false">
        <intent-filter>
            <action android_name="com.google.firebase.MESSAGING_EVENT" />
        </intent-filter>
    </service>

Looking forward to some expert suggestions.