Mo. Rev. Stat. § 339.160
No person, partnership, corporation, or association engaged within this state in the business or acting in the capacity of a real estate broker or real estate salesperson shall bring or maintain an action in any court in this state for the recovery of compensation for services rendered in the buying, selling, exchanging, leasing, renting or negotiating a loan upon any real estate without alleging and proving that such person, partnership, corporation, or association was a licensed real estate broker or salesperson at the time when the alleged cause of action arose.
(L. 1941 p. 424 § 16, A.L. 1993 S.B. 18, A.L. 2004 H.B. 985)