Hi, thanks for your question!
If you are on an annual plan and you add billable collaborators, that charge will appear on the next monthly billing date on a pro-rated basis.
For example: if you are one month into the annual plan and you add a billable collaborator, you’ll be charged on your next monthly billing date for the remainder of that year, from the date they were added as a collaborator.
A workspace will be billed for each and every billable collaborator – a billable collaborator is anyone that has greater than view/read only access.
For more on billing check out our Billing FAQ