add user

I have purchased and used 10 pro licenses, but since yesterday I have not been able to add users.
Why is that?

Add User MENU

User Type : Licensed

                       Zoom One Business(6available)

This is the text I see in the User Add menu
but When i click the "ADD" button,
the message shows up like this

You have exceeded the limit of license assignment for your account. Buy more licenses to increase the limit.