Using the Tor browser on amazon.com, everything appears normal, however, when you purchase something and hit "place order" you immediately get the confirmation email but amazon.com immediately cancels the order.
Amazon, Cloudflare and Google usually aren't a fan of Tor network. Google blocks connections from Tor (sometimes shows a captcha and let it go), Cloudflare keep asking to complete captcha and Amazon as you seen on your Tor browser cancels your order. They detect 3 layer of IPs which is suspicious to them so you can try reaching maximum privacy so they detect only Exit node's IP and there you go or not using Tor for these websites by bypassing them in your Tor Browser proxy settings
Note that 1) Tor is fine the problem is with Amazon 2) If you need help with reaching maximum privacy follow instructions at torproject.org 3) Tor Browser is basically Firefox so proxy settings is same as Firefox you can find out how to do it all over the Internet