Officially Gigante do Varejo does not yet accept cryptocurrencies as a form of payment, but there are some sites where you can exchange your cryptocurrencies or tokens for Amazon gift cards and make your purchases online.
Usually these sites serve some countries already defined, but it seems that your country is not in the list of sites, as long as Amazon delivers the product in your country, your Giftcards will be valid for you to use.
I will leave two sites that I found that seem very reliable for you to exchange your cryptocurrencies for GiftCards.
1 - SpectroCoin
If you don't have a SpectroCoin account yet, Click on this link https://spectrocoin.com/en/signup?referralId=zzd778dj and Register, it's really quick, you can use your Google or Facebook account
1.1 Access the Wallet Section and choose the cryptocurrency you want to make your deposit, there are several used by the website such as Bitcoin, Dash, ETH, XEM, XRP, Litecoin, Stellar.
1.2 Click WithDraw and choose the cryptocurrency you want to purchase GiftCards, then navigate to Refills and Vouchers
1.3 Choose your Country, scroll down a little bit to "Stores", choose an Amazon store to request a GiftCard
You will receive a validation code via email, SMS or 2FA from Google, Enter the Code for validation and press Enter
You will Receive a Code, now you are ready to make purchases on Amazon using your GiftCard, you just need to access the Amazon website, choose the item you want. As soon as you complete the purchase order, select as payment Amazon Gift Card and enter the code you received from SpectroCoin
2 - Bitrefill
Bitrefill serves about 170 countries, most likely your country will be served by it.
The Process is similar to that of SpectroCoin, just register on the site through this link https://www.bitrefill.com/?hl=en and follow the step by step that you can quickly exchange your cryptocurrencies for Amazon GiftCards
GiftCards at the moment are a good alternative while Bitcoin and Cryptocurrencies do not have mass adoption in commerce and services, so you can directly exchange your cryptocurrencies without having to go through Exchanges and Banking Institutions and lose part of your capital with many fees charged.
