According to a website: “Creating a book giveaway function does nothing but increase you and your book’s visibilities. Meaning that it is very necessary. Amazon has created a book-giveaway-channel that would allow authors to create reading contests, and choose their winner(s).”
If you create this type of giveaway through “Amazon Giveaway,” you must PURCHASE the prizes for your winners. And, you must PURCHASE those books from Amazon. Amazon is NOT going to buy those prizes for you.
Remember that, with most contests, the contest sponsors are the ones who reap the most benefit. I’m not opposed to giving away books to readers but you can probably get copies for a lot less through your publisher. And, you can host and promote your own contest on your own website and through your own social media accounts. I definitely don’t recommend paying full price to Amazon for YOUR OWN book(s).