There are two methods for assigning an existing device to a user. It is important to note that consumers can only have one of each of the following devices: analog phone, IP Phone, and external device. Depending on the devices the user already possesses, one or more items in the dropdown menu may be disabled.
Hi @Oya-Erdayı
did your purge the objects completely?
It looks like that you have still archived or deleted objects created for the object type.
If you have still archived, deleted or maybe unfinished objects you can purge them in the system administration of i-doit:
Administration → Systemtools → Cache / Database → Objects or Categories