Nuki Opener without intercom

Hello,

I am trying to use the nuki opener with our old door bell and switch buzzer.

The opener is working with our buzzer and opens the front door. But the ring to open function is not working. I tried to connect the green (yellow also) wire directly to our door bell. But the opener doesn’t recognize if someone rings the door.

If I ring the bell I can measure 10V AC and the door bell. Can anyone help?

Kind regards.