Shared Access Invite Not Working

I'm trying to set up my wife as a shared user. The initial invite comes through on her email just fine, but when the 2-factor code is "sent" by Ring it never arrives. Looking at the number of characters (some of which are masked) in the email to which Ring claims it's sending the code, it seems to have added an extra character in the domain name. Asking the app to send via another method, instead of offering something useful like an option for an SMS message, it simply brings up a login screen which then rejects all known combinations of emails and passwords. All our apps are up to date, yes we've turned everything (even the bloody kettle) on and off, tried to set my wife's account up on any number of different devices, uninvited then reinvited her etc ad nauseam. None of it works. Not impressed.