Navigate to People > Pending Invitation. This shows all the people you have invited to join BoosterHub, but who have not yet accepted their invitations and downloaded the app. Click Resend invite for each person, or choose Resend All as desired. There is nothing the Admin needs to do to “approve” a Member other than enter their information and send the invite; the Member joins the club by clicking the link in the email they receive.

However, if you created a Registration Page to allow people to become Members by filling out the form, then you will have to Approve them. They can be seen in the dropdown menu, and you can toggle between Invited/Approved and Members Needing Approval to see all the people who have not accepted the link to join BoosterHub yet.