Every agency of local government that acquires goods or services, or conducts any other type of contractual business with a nongovernmental, privately owned enterprise, shall promptly pay for the completed delivered goods or services by the required payment date. The required payment date shall be either: (i) the date on which payment is due under the terms of the contract for the provision of the goods or services; or (ii) if a date is not established by contract, not more than forty-five days after goods or services are received or not more than forty-five days after the invoice is rendered, whichever is later. Separate payment dates may be specified for contracts under which goods or services are provided in a series of partial executions or deliveries to the extent that the contract provides for separate payment for partial execution or delivery. Within twenty days after the receipt of the invoice or goods or services, the agency shall notify the supplier of any defect or impropriety that would prevent payment by the payment date. Unless otherwise provided under the terms of the contract for the provision of goods or services, every agency that fails to pay by the payment date shall pay any finance charges assessed by the supplier that shall not exceed one percent per month. The provisions of this section shall not apply to the late payment provisions in any public utility tariffs or public utility negotiated contracts.