"enable kelvin" greyed out in dashboard

[kelvinhub2]

Hi
I have about 40 lights, and for all but one, the "Enable Kelvin" button is greyed out in the "Kelvin Dashboard" view in "home": how can I enable them?
(I am running Kelvin in a Synology Docker , the installation seems to be running smoothly otherwise. Restarting - or waiting 12h - did not help)
Any help would be appreciated
Thank you in advance