Mo. Rev. Stat. § 417.412

Until payment for invention development services is made, the parties to a contract for invention development services have the option to terminate the contract. The customer may exercise the option by failing to make payment to the invention developer. The invention developer may exercise the option to terminate by giving to the customer a written notice of his exercise of the option. The written notice becomes effective on its receipt by the customer. Notwithstanding any contractual provision to the contrary, payment for invention development services may not be required, made, or received, before the seventh day after the day on which the customer receives a fully executed copy of the contract.