Silent Piano not recognized anymore by PT in Macbook

Hi,
I have been using pianotec for my silent piano and it always worked fine. I havn't been playing for a few months and all of a sudden, it doesn't work anymore. The Midi interface is recognized by my macbook though (I think..)
Because the tutorial video is for Windows user I can't find any help there.
Can anybody help me?

If I use the digital keyboard in the app it works just fine. So it doesn't have to do with my headphones.

I can make screenshots of whatever you need. I just don't know which would be helpful.

THANKS A LOT!

Kindly,
Franziska

P.S.: Sorry for my English, I'm not a native speaker (German).