To invite clients as Viewers, click on the “Members” tab on the left sidebar, then click “Invite member.”
Enter the email address of your client and set them up as a Viewer. How to limit client view to assigned projects only?
After your client has accepted the invite and is now in your organization, you would have to disable time-tracking for them if they are not going to use the desktop timer to track their own time. That way, they don’t count against the plan’s user limit.