Mo. Rev. Stat. § 432.030
Current with changes from the 2023 Legislative Session
All assignments of wages, salaries or earnings must be in writing with the correct date of the assignment and the amount assigned and the name or names of the party or parties owing the wages, salaries and earnings so assigned; and all assignments of wages, salaries and earnings, not earned at the time the assignment is made, shall be null and void.
§ 432.030, RSMo
RSMo 1939 § 3356