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 as a Subscribed User
To add a collaborator select "Management" and then "Plan". Some contacts that you have Shared on at least one project within your Studio that you "own" (i.e. that you've created) will appear for you to choose from, or you can add an email address manually.
Each potential collaborator is eligible to be added to your plan free for the first 7 days! Simply click "Add" next to their name, and confirm the subscription update.
If a collaborator has already had a free 7 day period and was removed from your plan, you can add them back as a paid collaborator at anytime. Charges for this collaborator will begin as of the date they are added.

Add a Paid Collaborator as a Free User
If you are currently a free user, you can select your collaborators once you've selected your plan, and completed your subscription. You can then add collaborators immediately or at any time during your subscription. Learn more about how to subscribe here.
Remove a Paid Collaborator
Note that "Un-sharing" 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 'Team Member’ button:
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 change or cancel your subscription, this too will apply to any paid collaborators on your account.