In Celtx, a 'Paid Collaborator' is a user whose subscription is paid for by another user. Collaborator 'seats' can be added and removed from your subscription at any time.
Add a Paid Collaborator
Before you can add a collaborator, they must be Shared on at least one project within your Studio that you "own" (i.e. that you've created).
Any users who are shared on one of your owned projects can be added as a collaborator via the "Plans" page, under "Management" then "Plan". Simply click "Add" next to their name, and confirm the subscription update.
If you are currently a trial user, you can select your collaborators once you've selected your plan and before confirming your payment.
Remove a Paid Collaborator
Note that "Unsharing" collaborators from all your projects does not remove them as a paid collaborator.
To remove a collaborator from your subscription, click "Management" and then "Plan". You will see all the paid collaborators on your subscription here. To remove a paid collaborator, hover over the ‘Added’ button and notice it gives the option to “Remove”. Select and confirm. They will be immediately removed from your subscription.
If you would also like to remove them from your Projects, consult the article on Sharing and Permissions.
Collaborator Subscription Type
When you add a collaborator, they receive the same subscription-type as you. If you upgrade your subscription, this too will apply to any paid collaborator seats on you account.