O.C.G.A. § 7-4-16

Unless otherwise provided in writing signed by the obligor, a commercial account becomes due and payable upon the date a statement of the account is rendered to the obligor. The owner of a commercial account may charge interest on that portion of a commercial account which has been due and payable for 30 days or more at a rate not in excess of 1 1/2 percent per month calculated on the amount owed from the date upon which it became due and payable until paid. As used in this Code section, the term “commercial account” means an obligation for the payment of money arising out of a transaction to sell or furnish, or the sale of, or furnishing of, goods or services other than a “retail installment transaction” as defined in paragraph (10) of subsection (a) of Code Section 10-1-2.