#N/A is when Excel is not finding the value being searched for
- Excel is not finding the part number in sheet "Product" which makes no sense whatsover
- the exact same list is used for data validation and for the search
- the value in A2 in the Invoice sheet comes from this list
OFFSET(Product!$A$2,0,0,COUNTA(Product!$A:$A)-1,1)
(which is A2 to the last cell with value in A in sheet "Product")
- Excel is looking for that value in the same sheet and column as generated the list (ie column A in "Products")
VLOOKUP(A2,Product!A:B,2,0) - column A
Which version of Excel are you using?
Post the part number Excel is not finding