Hello Stefan,
your “Administrator” should be member of the Group opsiadmin (and maybe opsifileadmins). Are you able to login via the webinterface https://<your-server-hosting-opsi>:4447 ?
There’s an older discussion (from 2017) in this forum but it may still help to reinitialize the current opsi config an restart the service(s).
Good luck!
Maik