This usually happens when a users original invite has expired. To fix this:
- Log into your Parentapps Portal.
- Go to Users and find the parents name.
- Select the tick box next to their name on the left-hand side.
- When you have done this, go to Group Actions on the right-hand side and select un-invite.
- This will remove all old invites from system.
- When you have done that, all you need to do is send over a new invite and this should solve the problem.