It doesn’t look as though Teufel have made a HTTP API so it will be very hard to control it outside the included app.
My suggestion would be to download some sort of internet package tracker similar to Wireshark on your phone and identify the HTTP requests the app is making to control the device. Identify the target address and content in the request, then send the same from OpenHAB.
Manufacturers protect against this though so that your smart home cannot be hacked, and sometimes make it impossible to do this.
Another way would be to use Bluetooth to control it. This is still a difficult way to do it though, would probably require an Arduino and some extensive programming knowledge to copy all the Bluetooth commands
It has google home control, maybe there is a way to create some rules/scenes linked to OpenHAB?
Thanks for the suggestions. Those were also my thoughts.
One point I disagree
Manufactures are usually not well protecting those interfaces, even when having cloud functions. However, it helps if the App just uses unencrypted http requests, which can be sniffed with Wireshark or tcpdump even the App runs on the mobile. I just want to check out other options before digging into this.