(a) Except as provided in § 15–105 of this subtitle, interest shall accrue at the rate of 9% per annum on any amount that:
(1) is due and payable by law and under the written procurement contract; and
(2) remains unpaid more than 37 days after a unit receives an invoice.
(b) Interest shall accrue beginning on the 31st day after:
(1) the day on which payment becomes due under a procurement contract; or
(2) if later, the day on which the unit receives an invoice.