Mo. Rev. Stat. § 408.236
Any person violating the provisions of sections 408.231 to 408.241 shall be barred from recovery of any interest on the contract, except where such violations occurred either:
(L. 1979 S.B. 305, A.L. 1988 H.B. 1355, A.L. 1994 H.B. 1312 merged with S.B. 718)