Amaon makes a distinction between invoices issued by Alibaba. You have to ask them for a sales invoice, not the one they normally issue becasue Amazon assumes people lie on the invoices for import tax reasons. I think it is part of an intentional attempt to shirk responsibility for Amazon losing our products, but that is what they require. Just have your manufacturer provide a sales invoice for shipped units on their corporate letterhead, make sure the product information is visible, clearly matches your product, and covers the time you had the item for sale on Amazon. You can hide the cost if you want. There is a help page on this somewhere. Dig for it and good luck. I also was told on the forum by someone (can't remember who) print the invoice, take a picture, then upload the picture. I think the bots like pictures better.

I started using a 3rd party app to audit my FBA products and they had better results than I have even without having to upload evidence. I take pictures of my shipments now because of this very reason. Even with pictures and invoices, it is a struggle. Amazon simply hides from their own employee theft or incompetence/loss of products. Keep an eye out for Amazon Warehouse selling your products.