Whether it's the merchant or the bank that's left holding the bag often depends on the particulars like whether it was a chip or a magstripe transaction, but th

Whether it's the merchant or the bank that's left holding the bag often depends on the particulars like whether it was a chip or a magstripe transaction, but the larger point is that in card-not-present scenarios you can't pay once without also exposing secrets that allow whoever gets them to make subsequent transactions without your permission. Better would be to have whatever secret authorizes spend (private key) be separate from the account identifier (public key) and to push money, rather than sharing a symmetric secret which authorizes whoever has it to pull money.