Unable to add a user management role

I want to add a user to administer their own number. I created a user account and then requested access by phone number. As the account administrator, there are no entries in the pending request section. I have waited a couple of days for it to show up. I then gave access to the entire account to that user. That worked. When I try to change that access to just the one account, the entry for that user disappears entirely. When I have the user account request admin access for the single phone number, it says there already is a request pending. Any ideas on how to proceed?