Help with FBA Proof of Ownership

Hi –
AMZ lost one of my shipments. I sell used electronics – I purchase many of these on eBay. They initially did not accept my eBay invoices as “Proof of Ownership.” Has anyone been down this road before?

Aside: Please no comments about how I “shouldn’t be purchasing items from eBay” – it’s profitable so I’m not really looking for business model advice. Just looking for any tips.