Reason 1: It may happen when user changes chart of accounts in the accounting system without syncing all DEAR transactions first.
Solution: If you made changes to the chart of accounts recently you need to tell us how to remap them back to the old account codes in DEAR. Email DEAR support at email@example.com
Reason 2: COGS transaction = 0 (for example if the purchase invoice for the items has not been authorized, or the cost of the items was set 0 during stock adjustment or stocktake).
Solution: Assign value to the stock by authorising purchase invoice or other relevant transaction.
To investigate this issue you might find it useful to use 'Movements' tab on the Product screen.