Via email. Likely reproduction instructions:
- Create a bot account firstname.lastname@example.org on your instance.
- Invite email@example.com via the manager-facing "Invite Members" tool.
- Get an error about "contact staff to import", since the email is already associated with an account.
- This is correct-ish, but not very specific/helpful.
- Get an error about "you probably accidentally created this user as a bot, contact staff to delete the account".