Cryptocurrency debit cards are a relatively recent development in the Blockchain world. They were invented to solve the problem of using digital coins for day-to-day expenses. Obviously, you can’t just go to your nearest grocery store and pay for your shopping list with Bitcoins, not yet at least.
This is very inconvenient because it introduces an additional difficulty of searching for a place to exchange your cryptocurrencies to fiat money before you can actually start spending them. There have been several proposed ways to make cryptocurrency spending a more direct process and plastic cards are one of them.
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https://cointelegraph.com/explained/what-are-cryptocurrency-debit-cards-explained