Okla. Stat. tit. 43, § 43-109.5: Voluntary relinquishment of physical custody –

Presumption.

When an order has been entered which provides for payment of

child support and the legal custodian places physical custody of the

child with any person, subject to the provisions of the Oklahoma

Children's Code or this title, without obtaining a modification of

the order to change legal custody, the placement of the physical

custody, by operation of law, shall create a presumption that such

person with whom the child was placed has legal physical custody of

the child for the purposes of the payment of child support and the

obligee shall remit such child support obligation to the person with

whom the placement was made.