If an item exists in pcs, box (say 24 pcs) and pallets (say 720 pcs).
When this item is setup to addd supplemetary items for example:
1 [bottle item] per pcs
1 [Box item] per box
1 [Pallet item] per pallet

When the purchase order reads

30 pieces of unit box (=720)

the result is that 30 pieces of Boxes are added to the PO - the system ignores the bottles and the pallets.

The setup could be changed to:
24 [bottle]s per box
1 [Box] per box
1 [Pallet] per 30 box

The result for 30 pieces of boxes would be the correct quantity for both bottles, boxes and pallets.

HOWEVER.
If the purchase order line instead read 1 pallet or 720 pieces. Nothing would be created

Suggestion:
Enable unit conversions when it comes to supplementary items