Mo. Rev. Stat. § 400.2-508: Cure by seller of improper tender or delivery — replacement.

(1) When any tender or delivery by the seller is rejected because nonconforming and the time for performance has not yet expired, the seller may seasonably notify the buyer of his intention to cure and may then within the contract time make a conforming delivery.

(2) Where the buyer rejects a nonconforming tender which the seller had reasonable grounds to believe would be acceptable with or without money allowance the seller may if he seasonably notifies the buyer have a further reasonable time to substitute a conforming tender.