How to pack multiple first level packing units into a parent packing unit

Summary:

Unable to pack first level packing units into a second level of packing unit

Content (required):

We have a requirement where we need to pack some semiconductor items in a box and then the few boxes will be further packed into a bigger box/case. We have defined the inner and outer box as container items in PIM and also defined the Manage default packing configuration with maximum weight.

Now, say we have a order line with base item of quantity 20. Each 10 quantity are packed into one inner boxes. So after we clicked on Action-> Automatically pack, shipment lines have been split into 2 each with 10 quantity and different packing unit number.