The City is not liable for the payment of interest pursuant to this subtitle: if a proper invoice for accrued interest is not submitted within 30 calendar days after the payment date of the amount on which the interest accrued; if there is a dispute between the City and the contractor; for more than 1 year following the 31^st calendar day after the receipt date; or on amounts representing unpaid interest. City Code, 1976/83, art. 1, §27A(d) Ord. 89-280