Proof of Purchase Invoicing for manufacturers

Hi,

We are hoping for some best practice and advice. We are (new) to Amazon and have gone through Seller University and forums and wanted to confirm what best practice is for FBA reconciliation and invoicing as a manufacturer. It seems Amazon require a proof of purchase to investigate one of our ASINs. In our line of products, we are the manufacturer so therefore, it seems the advice is that we have to invoice ourselves? i.e. one entity of us as the manufacturer and then our Amazon name as the buyer? We operate from the same address and we would issue a wholesale invoice for the wholesale value from ourselves (manufacturer) to ourselves (buyer) which matches the inventory shipped / descriptions? Is this correct or is there a better way of going around this?

Thanks