Mo. Rev. Stat. § 436.321

If it is determined that a subcontractor's performance has been satisfactorily completed and the subcontractor can be released prior to substantial completion of the entire project without risk to the owner involving the subcontractor's work, the contractor shall request such adjustment in retainage, if any, from the owner as necessary to enable the contractor to pay the subcontractor in full, and the owner shall as part of the next contractual payment cycle release the subcontractor's retainage to the contractor, who shall in turn as part of the next contractual payment cycle release such retainage as is due the subcontractor.