A $0 GPRO can severely affect your inventory value, especially if that item is consumed before the AP invoice corrects it. Below is a simple Alert that can help manage when those sneak into the system.
SELECT T0.[DocNum], T0.[DocDate], T0.[CardCode], T0.[CardName], T0.[NumAtCard] FROM OPDN T0
INNER JOIN PDN1 T1 ON T0.DocEntry = T1.DocEntry
WHERE T1.[LineTotal] = '0' AND T0.DocDate=cast(GetDate() as DATE) AND T0.[DocStatus] = 'O'