We had a single license for an expensive app and it was assigned to a
user account. When we assigned it to the device we received the error
that the OP reported. I searched VPP Content from the Mobile Devices tab
to find the assigned user, and remove...
We haven't, and we're finding that PowerSchool has assigned the same ID
(which would end up being the "person_id") to some teachers and
students. Has anyone else seen this?