I think the default port that deCONZ uses is port 8080 which is already occupied by OH itself.
Because of this a so called override.conf can be created:
/etc/systemd/system/deconz.service.d/override.conf
Thank you all for replying so quickly.
There is clearly a big community behind openHAB.
It appeared that deCONZ was running on port 80.
Used the integrated install mentioned by msstormi to overwrite the install to port 8081.
First I tried to add the override.conf file as suggested by Wolfgang_S.
But no FTP access, and my linux skills are too limited to do this through the CLI.
Seems I can still learn a lot here.
Thank you for setting me up. I’m afraid this won’t be my last question.