Can my clients be external collaborators for my zipBoard project?
Yes, you can share your project files with your clients by simply sharing a link. With the shared link, your clients can review your work and can share their feedback. Your clients would not have any access to the activity of your internal team but still, you can keep them posted for all important updates and can ask for their reviews at any phase of project lifecycle with the share link. To know the stepwise process and different share options visit here.
If you just wish your client to have access to the feedback and permission to approve or reject it. Then you can add your clients as 'Client' to the zipBoard project.