Mo. Rev. Stat. § 454.624: Payment of benefit due, discharge from liability.

In the case of any claim submitted by the custodial parent for care provided to a minor child who is enrolled as an eligible dependent pursuant to an order or notice of health benefit plan coverage, the health benefit plan administrator or insurer shall, in the absence of an assignment of benefits to the health care provider with respect to such claim or proof of payment by the noncustodial parent, pay to the custodial parent any benefit due. The health benefit plan administrator or insurer shall be fully discharged from any and all liability on the claim to the extent of such payments to the custodial parent.