Siedle BTS 850-02 stuck at "press door opener"

I just had the bell system in my building repaired, after it was defective for a while. When I tried setting up the Nuki Opener again (which worked before), I am now stuck at the setup step “press door opener”.

The Opener recognizes a button got pressed and it’s LED changes the pattern of flashing, but the app just stays at the same step, without me being able to continue any further.
The door opener on the intercom itself, with the opener attached (and without, as well) works just fine.

I got a Siedle BTS850-02

I can only put one Image in this post, so I removed the image of the wiring before installing the opener.

this is after installing the opener:

I also tried switching to basic wiring, with only the red and black wires of the opener being connected (and the original ones, ofc). I also tried selecting Generic Bus (siedle) instead of BTS 850-02 in the setup, but nothing helped.

this is the original wiring: