Why Does My Card Not Work to Buy Crypto?

Usually because your bank has a rule about the whole category and your card falls under it. Crypto purchases carry merchant category code 6051 - "quasi-cash", the same drawer as casino chips and money orders. A bank that is uneasy about crypto does not have to block Coinbase or Kraken one by one; it switches off the drawer. Nothing about you, your balance or your credit history is involved.

A policy block and a fraud flag are different animals

A fraud flag is about this one payment. Something looked odd, the bank paused it, and confirming the payment in your app clears it in a minute. A policy block is about every payment of this kind, forever. Several banks have published such bans outright - Chase's UK arm and Starling among them - and no phone call lifts them. You can usually tell them apart by the pattern: a fraud flag comes with a text or an app notification, while a policy block gives the same instant refusal at every amount, every time.

Why the debit card works and the credit card does not

Same bank, same person, different rulebook per card. On the credit side, quasi-cash is treated as a cash advance: an extra fee, interest from the first day, and no interest-free period. A lot of issuers would rather refuse the transaction than explain the bill, so they do. The debit card from the identical bank often sails through, because nothing is being borrowed.

Cards that rarely work at all

Prepaid cards, gift cards and most single-use virtual card numbers are refused by nearly every on-ramp, because the platform has to tie the card to a verified identity and those cards deliberately break that link. The same goes for a card in a company name or someone else's name, even a partner's. American Express is unsupported at many crypto on-ramps regardless of the bank behind it.

If the block turns out to be policy, stop fighting the card. A bank transfer is coded as a transfer rather than quasi-cash, clears the same compliance checks, and usually costs around one per cent against the three to five a card adds. One thing never to try: describing the payment as something other than what it is. That breaches your account terms and risks the account, not just the purchase. The full list of decline reasons covers the fixable causes, and debit card declines deals with the smaller traps on the debit side.