Mo. Rev. Stat. § 339.160
No person, partnership, limited partnership, limited liability company, professional corporations, corporation or association engaged within this state in the business or acting in the capacity of a real estate broker, real estate broker-salesperson 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, limited partnership, limited liability company, professional corporation, corporation or association, or its member, manager, officer, general partner or associate, as applicable, was a licensed real estate broker, broker-salesperson or salesperson at the time when the alleged cause of action arose.
§ 339.160, RSMo