FAQ

Activating

Accounts limit

java.lang.IllegalStateException: Not allowed to set the device owner because there are already some accounts on the device

You should remove all accounts on your device

Users limit

java.lang.IllegalStateException: Not allowed to set the device owner because there are already several users on the device

You should remove all users on your device

Clone app, children space etc.

They are actually users, remove it

MIUI limit

java.lang.SecurityException: Neither user 2000 nor current process has android.permission.MANAGE_DEVICE_ADMINS.

You should open USB debugging (Security setting) in developer options. Execute activating command with superuser can bypass this limitation