When inviting members to join your community and/or space, if the "email" of the invited user already exists, give a message/warning/notification prompt right away that the user already exists.
See the support thread for the context of what could have been avoided:
https://bettermode.com/hub/community/ask-for-help/post/invites-sitting-in-invite-queue-how-and-where-do-i-see-this-queue-9SkmpaMhetq3UA2#comment/lance-korsun-add-it-to-the-wishlist-i-completely-agree-with-that-idea-VsFF9O2jJKSoD6s