Thanks for your messages.

I have already install twisted but without "sudo".
I reinstall it with "sudo pip3 install twisted" and now the service run automaticly at startup.

Thanks for your help.

Hello,

I have the same probleme than micksel.

If I start it manually everything works fine:
/home/pi/domoticz/plugins/IKEA-Tradfri$ python3 tradfri.tac

But if I try with ikea-tradfri.service

pi@raspberrypi:~ $ sudo service ikea-tradfri status
● ikea-tradfri.service - IKEA Tradfri COAP-adapter ...