Mo. Rev. Stat. § 71.625

71.625. License tax, payment, when deemed timely — municipal corporations, interest and penalties on delinquencies to apply. — 1. The timely payment of a license tax due to any municipal corporation in this state, or any county pursuant to section 66.300 , which is delivered by United States mail to the municipality or county office designated by such municipality or county office to receive such payments, shall be deemed paid as of the postmark date stamped on the envelope or other cover in which such payment is mailed. In the event any payment of tax due is sent by registered or certified mail, the date of the registration or certification shall be deemed the postmark date. No additional tax, penalty or interest shall be imposed by any municipality or county on any taxpayer whose payment is delivered by United States mail, if the postmark date stamped on the envelope or other cover containing such payment falls within the prescribed period on or before the prescribed date, including any extension granted, for making the payment. When the last day for making any license tax payment, including extensions, falls on a Saturday, a Sunday, or a legal holiday in this state, the payment shall be considered timely if the payment is made on the next succeeding day which is not a Saturday, Sunday or legal holiday.

2. Except as otherwise provided by law, the interest provisions of section 144.170 and penalty provisions of section 144.250 relating to delinquent sales taxes shall apply to delinquent taxes due as a result of the imposition of a license tax by any municipal corporation. The limitation for bringing suit for the collection of the delinquent tax and penalty shall be the same as that provided in sections 144.010 to 144.510 .

(L. 1998 H.B. 1301, A.L. 2012 H.B. 1504)