Sending in Case Packed and indivual items in one box - how do you blimmin' do it?

What's the correct way to send in Case Packed items and single units in one SPD?

Can anyone point me to a YouTube or Amazon university guide - Amz call it 'Optimised by Box-Level Placement.'

because I've been sending in boxes inside bigger boxes and when those labelled boxes inside go missing, it's a complete pain in the backside as Seller Support say they have no record of the inside boxes being picked up - I must be doing something wrong.

Any help greatly appreciated

Anyone from AMZ admin help out here please? @Winston_Amazon @Julia_Amzn

Perry