In reply to JR:
> It's there to protect the vendor, you could authorise the card to take fuel, and use the card in the shop before the fuel has been charge. The money is gone and the card can't be charged beyond its top-up amount, nor will the card issuer guarantee the payment.
I noticed several times that I used the Revolut card for payment and, literally, within seconds I heard a message alert on my phone, I went to the Revolut app and found that the transaction had gone through.
I must admit that the only problem occurred when I tried to use it for a fiver's worth of refreshments on easyJet. There was still about £100 on the card but it was declined.