It will be necessary for the vendor to collect from, or charge to the customer the entire amount of the tax as computed on the selling price in each case of an installment or credit sale, irrespective of the amount of the installment or down payment made by the purchaser consumer or whether any installment or down payment is made. Installment and credit sales together with the tax applicable thereto must be reported on the vendor's return covering the period in which the installment or credit sale occurred.
Okla. Admin. Code § 710:65-19-160