and try the feature again, remembering to log the other one out before I ask the system to shut down.
If all the other user are logged out, it will not bother you with that prompt.
I'll repeat here.
short user name of an administrator -- let's say it's myadminer
password of the this administrator -- password for myadminer
I always log onto the user mac.
I have always shut down from user mac.
With the prompt, I enter mac with mac's password.