Approved Pickups and Guardians ARE able to add banking information and set up auto-pay if they wish to make payments. HOWEVER! Anyone listed under this category will NOT receive invoices or be able to see invoices on their dashboard.
If this person wishes to have full access to the billing function, their role needs to be updated to Parent. The only way to pay invoices as an Approved Pickup or Guardian is to have auto-pay on as they will not have access to manually pay invoices.
As a troubleshooting tip: if a parent is letting you know that they can't see their child's invoices, it is likely that they have been set-up as an Approved Pickup or Guardian and need to have their status changed on the Student's Profile.