I purchased a plan for up to 10 users and currently have 8 managed users and 1 external user, yet I cannot add new users.
Though I have 8 managed users, console says 9 managed users. When I try to invite a new user, I get the following error: “You have reached the seat limit for your plan.”
Probably because I invited a user who is already connected to another company. However, the invitation cannot be revoked since the target user does not appear in my admin console.
Hi
It’s possible that the issue is due to a recently deleted managed user from your account who has not yet been fully removed from our database. Please try adding the new user again after an hour or two. If you encounter the same error, let us know so we can raise a support ticket for further assistance.
Regarding your plan, both managed users and external collaborators count toward the total number of users. I suspect that the user who already belongs to another company is currently listed as a collaborator. You can check this by navigating to Admin Console > Users & Groups > External Users.
From there, you can remove the user if necessary, and then add another internal user from your organization, if applicable.
I look forward to your response. 
Hi Jey,
It's been over 24 hours, but the BOX user console still shows 9 users in total—9 managed users and 0 external users (see attached screenshot).
However, I’m still unable to add a new user and am receiving the same error message as before.
Could you please help raise a support ticket with BOX regarding this?
Thanks in advance,
TY
Dear
I have submitted a ticket on your behalf. You should receive an email with the ticket #. For now, please keep an eye out for an email follow up from our Product Support who will continue assisting you.
Have a great day! 
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