Why training course think that it is wrong formula?
Confirmed Purchase Order Receipt (INV01 Inventory Ordering)
IF Confirmed PO Delivery > 0 THEN OFFSET(Final Shipment Amount, -Final Shipping Time Weeks, 0) ELSE 0
Although it looks like the correct formula but if you have finished your level 2 and you are taking up L2 final exams then it indeed is wrong, because you will have to replace OFFSET with POST. That is why this exercise is very helpful as it helps you to understand the limitations of OFFSET and the use case of POST. Please go back to the training and follow the order because immediately after using OFFSET there is another exercise which asks you to replace OFFSET
Note: POST will not take three parameters in its syntax, only 2.
Hope that helps