I recently deleted a user within our system. Upon trying to re-add the user, I am getting an error that the email is already in use, even though their account was already deactivated. Any tips on how to re-add this user?
You cannot delete users in Metabase - you can only deactivate them.
So you should enable the user again in Admin > People > click "Deactivated users" > find the user to activate again: