Can i continue to calculate AP turnover if the difference from ending inventory - beginning inventory is a negative number?

Inventory Purchases = (Ending inventory - Beginning Inventory) + COGS

beginning balance was 9,497

ending inventory balance was 8,992

8,992 - 9,497 = -502

COGS = 54,864

Since:

Accounts payable turnover:

Inventory purchases

Average Accounts Payable