Invoice amazon. Free shipping on qualifying offers. I sent them in two recent invoices for a few thousand. My local distributor gives hand written invoices to all walk in customers so the bogus claim of fake on a return and amazons recent crack down i seem a bit stuck.
Are you trying to upsell or charge additional shipping. This is only true if you are vat registered and it is a business to business transaction. They give you a packing slip with the delivery address on it.
You are running a business and therefore required to provide an invoice whether you are vat registered or not.