(1) A person defaults in the payment of a payment plan if an enforcement agency or the Secretary (as the case requires) does not receive a payment in accordance with that plan within 14 days or a longer prescribed period (if any) after the due date of the payment.
(2) If an enforcement agency or the Secretary does not receive a payment within the time specified in sub-section (1), the agency or Secretary (as the case requires) must send a written notice to the person to whom the payment plan applies advising that person of the default.