As I understand it, cash is only for face-to-face purchases.
According to the nostr:npub1kdkl4prkt7jmy8cdzdutqv8988vekl93nj4r25zpqpa5uacm9jkqnsjzq5 website
“Amazon eGift CardsPermalink
Amazon eGift Cards are one of the more private payment methods on RoboSats. They tend to be quick and convenient, but funds must be spent on Amazon.”