Missouri Revised Statutes Title XXXVI. Statutory Actions and Torts § 535.060. Demand of rent good, when

Any demand of rent, or rent and possession, by a landlord or the landlord's agent shall be deemed good within the meaning of this or any other statute of this state, when made at any time after the right to rent and possession accrues or the rent becomes due according to the terms of the agreement, whether by written lease or otherwise.