I’ve just come across the same issue. I think that the documentation needs to be updated to reflect this change. Currently it says this:
Manager: Other OFN users who have been granted permission to manage this account. If they don’t already have an OFN account, you can type in the new manager’s email as the notification email (see above), this will prompt them to get a confirmation email, and upon confirmation they will become a manager. If they’re already a OFN user, type their full email in the manager field.