How are private users defined?

[Darren_Murphy]

Yes, quite possibly. The below might be worth a try:

Private User Limit

Not on a free plan, I’m afraid. The only other thing I can suggest is if you think you know which other emails might have been used to sign into the App, you could try purging them with the “Delete User Data” option (found under Settings → Data). I don’t know whether or not this would have any impact (I suspect it won’t), but it might be worth a shot.