Mo. Rev. Stat. § 341.050

Said board of examiners shall, within ten days after their appointments, meet, and shall then designate the times and places for examination of all applicants desiring to engage in or work at the business of plumbing within their respective jurisdiction. Said board shall examine said applicants as to their practical knowledge of plumbing, house drainage and ventilation, and if satisfied of the competency of such applicants, shall thereupon issue a certificate to such applicant authorizing him to engage in or work at the business of plumbing either as a master plumber or employing plumber or journeyman plumber. The fee for a certificate for a master plumber or employing plumber shall be five dollars; for a journeyman plumber it shall be one dollar. Said certificate shall be valid and have force throughout the state and shall be renewable annually, and all fees received for said certificates shall be paid into the treasury of the city where such certificates are issued.