When you go to pay for something online with your Capital One card we'll sometimes ask you to enter a one-time passcode (or OTP for short), so we know it's really you.
It's a unique 6-digit number that we send as a text or automated voice message to the mobile or landline number of your choice.
This is to protect you from fraud. It means that even if your card details have been stolen they still can't be used to buy things online. So it's as secure as using your card in a shop.