When a credit card fails, the subscription is suspended. When the card is updated, the subscription starts up again. If the payment it failed on was the first one, it starts with that payment; otherwise, it starts with the next payment after the one it failed on. So you'd want to record in your database when each payment comes in, so you know whether to charge the missing monthly fee with AIM or whether to just do a $0.00 (Visa) or $0.01 transaction with void to verify the card.
