Transactions are carried out over an HTTPS link established by Revolut (currently used by over 20 000 marchants) between the customer and the payment server.
The sensitive data (credit card number, expiry date,...) are entirely encrypted and protected in SSL, in SSL, cannot be intercepted by a third party during the transaction. Revolut relies on a secure infrastructure approved by Visa, Mastercard, and the Groupement of Bank Cards according to the PCI-DSS standard used by banks.
The authentication with certainty of the cardholder is carried out by your bank (with the 3D-secure system), usually by the transmission of a code by SMS.