Walmart gift cards cannot be used on Amazon or any other online store or even at any other store other than Walmart.
Walmart Gift cards are not like a prepaid debit card that can be used on Amazon or other stores or anywhere else.
When someone buys a Walmart Gift card for someone that Walmart Gift card will only be able to be spent at Walmart stores or Walmart online.
You can buy gasoline at Walmart Stores with the Walmart Gift Card or anything else including cigarettes etc.
But you cannot use a Walmart Gift card on Amazon.
If you want to give someone a gift card they can use on Amazon you need to buy an Amazon gift card or buy the person a prepaid debit card that is a gift card that can be used anywhere.