Hello Taifun,
I had an Android App built just for Push Notification and it receives the msg form OneSignal but I don't see this App listed in the "Notification access" screen in order for me to select it when I use TaifunNotificationListener.StartService.
I'm not sure, if I understand your question?
Make sure to build the project before using it...
What happens, if you use the notification listener example project, build it and click Start?
And which device and Android version are you using for your tests?
There was something wrong with your test app yesterday. I downloaded 3 times and 3 times App Inventor could not open it. I just tried again and now it opened. I created APK. Installed in my Phone and it works fine.