When you add a user to a Teamup calendar, they will be sent an invitation via email to access the calendar.
If this individual doesn't have a Teamup user account, they can follow the link in the email invitation to activate their account, then log in and access the calendar.
If they don't respond to the email invitation, eventually it will expire and the link will no longer be valid.
If this happens, you can resend the invitation email:
Open Teamup in a browser.
Click the blue menu (top right) and select Settings.
Go to the Sharing tab.
Find the user in the list of users, links, and groups.
Click to edit the user.
Click on “Resend invitation” below the individual’s email address.