then the deduction with respect to the contested amount shall be allowed for the taxable year of the transfer.
Example: O Corporation makes its return on the basis of a calendar year and uses an accrual method of accounting. O receives a large shipment of typewriter ribbons from S Company on January 30, 1964, which O pays for in full on February 10, 1964. Subsequent to their receipt, several of the ribbons prove defective because of inferior materials used by the manufacturer. On August 9, 1964, O orally notifies S and demands refund of the full purchase price of the ribbons. After negotiations prove futile and a written demand is rejected by S, O institutes an action for the full purchase price. For purposes of paragraph (a)(1)(i) of this section, S has asserted a liability against O which O contests on August 9, 1964. O deducts the contested amount for 1964.
26 C.F.R. §1.461-2