Are you actually claiming that the Afterpay T&Cs are wrong?
The late fee is per item. If you have 20 overdue items you pay 20 separate fees. If you don't pay in 7 days you are charged an extra $7 per item ($140)
APT must be rubbing there hands with glee seeing all the ignoramuses thinking they only pay a maximum $10 a year in late fees. In fact they are potentially paying hundreds in fees for one missed payment.