deCONZ on raspi exits with error - starts correctly if initiated via console

Hi everyone,
I am running the Conbee II on a raspbian (PI 3+) bullseye with fhem installed. I can’t get it running with “normal” start through the systems processes.


● deconz.service - deCONZ: ZigBee gateway – REST API
Loaded: loaded (/etc/systemd/system/deconz.service; enabled; vendor preset: enabled)
Active: inactive (dead) (Result: exit-code) since Tue 2023-11-21 09:17:52 CET; 1s ago
Process: 1064 ExecStart=/usr/bin/deCONZ -platform minimal --http-port=80 --dev=/dev/ttyACM1 (code=exited, status=217/USER)
Main PID: 1064 (code=exited, status=217/USER)
CPU: 27ms

since this does not work, the web-app does not work as well and my Conbee II is not visible or accessible.

If I stop the service and start it via console (/usr/bin/deCONZ -platform minimal --http-port=80 --dev=/dev/ttyACM1) it does start and is accessible via the web-app.

What do you need except for this information to help me with this issue?
Do you have any hints for me what to do to start deCONZ with systemstart and get it running?

Does it make sense to implement and configure fhem with deconz just right now, when started via console? Or should I wait until deconz starts regularly with the system?

thank you in advance