"Past due" means the most recent renewal charge didn't go through — usually an expired card, insufficient funds, or a temporary block by your bank.
Your priority status isn't revoked the moment a charge fails, but Priority Review may stop covering new applications while the subscription is past due. We never add fees or interest to a failed payment.
You can cancel a past-due subscription the same way as an active one — one click on /applicant/subscription, or the cancel link from /help/cancel-subscription — and nothing more will be charged. To keep it instead, send a change request (/help/change-request) and a person will help you update the card.
Send a change request: billing mistakes our records prove are refunded automatically, and a person answers the rest within two business days.