Once a guest enters their details or clicks "Authenticate" from their email, they will be prompted to verify the transaction.
This usually happens in one of two ways:
SMS Code: A secure code is sent to the phone number linked to their card to be entered on the checkout page.
Bank App Approval: A push notification is sent to their banking app for a one-tap approval.
Bank Redirect (iDEAL): The guest is temporarily redirected to their own bank's website to sign in and confirm the payment.