Sorry, the user is always wrong. I couldn't find it because Amazon's UX is infallible.
If I can't find it, and I'm actively looking for it, there' something wrong with the page. It is not obvious like DoorDash is obvious. I don't think you can argue that in good faith.
Then either you weren't trying very hard or you need to put your glasses on. It's in the same place on every listing that has Add to cart/Buy buttons: under those buttons, after the "Secure transaction" link.