If you ever make an application which gets downloaded millions of times I cannot imagine you crafting millions of invoices for every single sale...
How about this: One invoice, which defines the app as one product, which you have sold x times? Like an app which is $10 each, app x 10000, which is equal to like $100,000?
Besides, invoices are means of negotiating payment, if I'm not incorrect, invoices are never legally required to be produced (at least in many countries), but if those are, all of those must︀ be held in the books.