Amazon denies my invoices from the manfacturer

FBA is a bad deal for sellers. Besides all the time it takes to pack and send your items, and then usually there are issues with items getting lost or damaged, and the utter hassle it is to get any compensation from Amazon over it with their ridiculous invoice scheme - besides all that, which is a heck of lot of trouble to begin with, after a few short months your items then start getting charged storage fees. You are then encouraged to cut prices to sell faster, and the storage fees get higher the longer you keep the items there until finally you might as well just pay to have them returned to you. That's one scenario. In the other scenario your products are selling well so you decide to up the price, only have price controls kick in, and your item is delisted as a "price error" with no real hope of getting it relisted even if you lower your price. Of course no company that respects the free market should be involved in controlling prices that sellers choose for their own products, but Amazon doesn't believe in the free market - they do believe in price controls, and any price that goes up too much, even if the item is out of print yet still in demand, finds itself delisted as a "price error" (nice euphemism). And once it's price errored out you then have to pay to have it shipped back to you.

As we all know Amazon doesn't pack protectively and the chances of that item getting damaged on the way back are not small. If it does get damaged and you ask for compensation you again have to go through the invoices scheme and if you're given any compensation for your now damaged item it'll be a fraction of what you were asking for the item and you'll likely even get less than you paid for the item.. So, like I said - - - FBA is about the worst deal there is for sellers. It's a lot better to save yourself the headache, time and loss and only do Fulfilled by Merchant.