Mo. Rev. Stat. § 433.050: Interest due on amount paid by surety.

When any bond, bill or note for the payment of money or delivery of property shall not be paid by the principal debtor, according to the tenor thereof, and such bond, bill or note, or any part thereof, shall be paid by any surety thereto, the principal debtor shall refund to such surety the amount or value so paid, with interest thereon at ten percent per annum from the time of such payment.