Okla. Admin. Code § 710:65-19-103 – Finance charges

(a) "Gross receipts" or "gross proceeds", as the case may be, does not include finance charges, carrying charges or interest charges on conditional sale contracts or other contracts providing for deferred payments of the purchase price, if the amount of such finance charges, carrying charges or interest is in addition to the usual or established cash selling price, and such amount:
1. (1) Is segregated on the invoice or bill of sale, or
2. (2) Is billed separately to the customer.
(b) Unless the conditions described in subsection (a) are met, such charges shall be deemed to be part of the gross proceeds or gross receipts for the purpose of computing the tax. [See 68 O.S. §1352]