With the new beta, I am able to open my door via App! 
I made the following mistakes during my first installs:
- I didn’t close the intercom for testing. I left it open … DON’T test with an open intercom.
- I removed the black intercom cable
After fixing this, I was able to get into the first steps of configuration in the app. But at the point, when Nuki wants to configure Ring to open it failed. But I answered the question “Has Nuki opened the door?” with yes, that is the only possibility for me to finish the setup assistent and only opening via app is possible, now.
