I'm currently a bit frustrated and I hope you could help me. I've bought a Popp Wall Controller looking like this:

I've paired it successfully with my z-Wave network and it shows 4 switch devices for it.
BUT they do not change their stage from on to off... they only send on.
What I want to archive:
When I press one of the 4 switches, it should switch on a wall plug - when I press the same button again, it should switch it off again. I do not want to use two different switches for on and off...
- I've tried to set the id of the wallplug in the "Groups and Network" page, but this seems not to work.
- I've tried to use a Group and also a Scheme, but (because the wall controller only sends on) this also doesn't work.
- I also tried to use a lua script, but I'm not good in LUA... my idea was:
...
when switch 1 is pressed and wallplug is on:
turn wallplug off
...
Would be great if you could help me to use this wall controller.
PS: it seems also similar to the Z-Wave.Me Popp KFOB-C Remote Control.
Greetings
Kel