Speedy Co is a well established company. The company's principal business is the production and bottling of '8 Down', a soft drink, which it carries out under licence. A royalty is payable to an Indian company computed at 7.5% of annual revenue of 8 Down and is payable one month after the financial year-end. The draft financial statements for the year ended 30 June 20X1 include an accrual for commission payable in the sum of $40,000 in respect of 8 Down sales for the year to 30 June 20X1. The auditor has completed his audit of the sales cycle and has concluded that total sales are not materially misstated.

Which of the following procedures, by itself, may provide sufficient audit evidence to verify the figure for royalties charged to the statement of profit or loss and other comprehensive income?