If you have a gift card, and you want to sell it in exchange for some crypto, then there are a couple of sites that will help you do that. You give them the gift card's info, and they'll pay you in cryptocurrency. Note that these sites won't give you 100% of your gift card's value, as they need to profit, and some gift cards have a better value rate than others. The following sites I'll be listing are the ones that I found. There may be more sites, but they are blocked in certain regions :  

• EJGiftCards : On this site, you can both sell and buy gift cards. Note that this site hasn't yet updated its descriptions and FAQ to mention that they support bitcoin payout, but they do. To sell one, you need to register, then click on the top “sell gift cards” button. You search for the brand and see if it is available, if it is you then provide the price amount available in the gift card, and you then get an offer. If you accept the offer, you fill in the gift card's details, and then put in your BTC address or PayPal. It may take them a couple of days to process it, then it will be put in the “payment-initiated” status until you get your payment. Their payouts are usually the upcoming Friday or the one after that. My payment was late until Monday though for some reason, but I did get it in full.

• SellGift : on this site you can sell and buy gift cards too. You register, then click the top “sell gift cards” button. You choose one of the available brands and the price amount of the gift card to get an offer. Then you fill in the gift card's details, and it'll process for up to a couple of days until it is validated. Then, when you get the money in your balance, you will be able to withdraw it from your profile. Supported withdrawal cryptos are USDT, BTC, and ETH.

• CoinCola : This is a trading site, and there is the option to buy crypto using your gift cards as a payment method. The offers are made available from various traders. The transactions happen manually through a chat on-site where you give them your gift card info, and then they release the BTC into your account's wallet. From there you will be able to withdraw it to your actual wallet, and the site supports various cryptos. Note that for some reason, they do not support BTC addresses that start with “bc1”, so you need to get your legacy address starting with “1”. I tried this site once, and it worked, but I still don't have the minimum withdrawal amount. Make sure the trader you pick has a high amount of completed trades and also a high rating as to avoid potential scammers.

These are the sites I know of that let you sell your gift cards in exchange for crypto. Hope you found this helpful. And thanks for reading!