Ah. I never purchased on Amazon for thousands. Maximum was probably a tad under 1000€, and these are so rare and years ago that I would not swear that an extra confirmation was not needed (but nor 3DS but at best the CVV)
For a few hundred I was not checked (that one I am sure)
Are your purchases in the thousands getting through?
https://docs.stripe.com/payments/3d-secure/strong-customer-a...