Mo. Rev. Stat. § 506.372: Monthly payments.

If the court has entered an order for payment of fees in installments pursuant to section 506.369, the offender shall make monthly payments to the department of corrections of twenty percent of the preceding month's income credited to the offender's account until the fees are paid in full. The department of corrections shall forward payments from the offender's account to the department of revenue for deposit to the general revenue fund until the fees are paid in full. The department of corrections shall establish written guidelines for the priority of payment consistent with state and federal law.