KNX for Homey - It won't work!

Hi guys!
New Homey owner here. Got it mainly because I recently bought a house with KNX. Downloaded the app and connected to the IP interface… and now I’m stuck.

I do not have an ETS license but I’ve gotten help to scale down the project file so I can use it in ETS Demo, which means I can find group addresses and such.

I can connect Homey to the IP interface and I can find, for example, a switch via “learn mode” and toggling the physical switch on and off or I can add the group address manually, it makes no difference:
When I push the created virtual button in the Homey app, nothing happens. Well, almost nothing; I can see the red LED light (TX) flash on the physical interface every time I push the virtual button so I know Homey is sending something to the bus. The command never reaches its endpoint though.

I can’t scan the bus for traffic because when I do, I get an error message saying the interface can’t accept any more connections.

I can’t for the life of me figure out why this is not working.
PLEASE help me, I’m getting desperate here…

@Crowntwig You probably need to download the application to the IP Interface. Often this will require a KNX USB Interface initially.