How to add current CRM users to a New Zoho Mail setup with the same domain?

I've looked but can not find a solution, just other unanswered questions. My problem; I setup my Zoho CRM account before setting up Zoho Mail and now when I try to add users to Mail, with the same domain, which has been accepted by Mail, I now get the infamous "user already exist" error, which sends out the Invitation to join that contains the other fun error

Note : You're already a member in Organization. Please contact your organization's Admin "user @wcarclub.com" to dissociate you from the existing organization. Once you're dissociated, you'll be able to accept this invitation and join the organization.

Does anyone know how to resolve this? I tried "dissociating" the user but I still receive the same error.