Collaborate is the part of issuu Optimum plan, so the editor of the publication will need to sign up for the Optimum plan to use this feature. Collaborate can be used with Premium plan as well with limited access.
Team members that are invited to an editor’s publications do not need the Optimum plan, but they do need a free issuu account to join the workflow in Collaborate. Anyone can create a free account on issuu.com.
You can sign up for the Optimum plan on our Pricing page.