Mo. Rev. Stat. § 321.260
The board in certifying annual levies as herein provided shall take into account, in addition to the amounts necessary for general purposes as herein provided, the maturing indebtedness for the ensuing year as provided in its bonds and the interest on bonds, and deficiencies and defaults of prior years and any contractual obligation and shall make ample provision for the payment thereof. In case the moneys produced from such levies, together with other revenues of the district are not sufficient to pay punctually the annual installments on its bonds and the interest thereon, and to pay any defaults and deficiencies on any such bonds or contracts duly approved by the voters of the district, then the board shall provide for such additional levying of taxes as may be necessary to pay for all such, and notwithstanding any limitations, such taxes shall be continued to be levied until the indebtedness of the district shall be fully and currently paid.
§ 321.260, RSMo