Cashback is available only for new Revolut users, who have not previously had a Revolut payment account but have successfully created one.
If the purchase is eligible for cashback, Revolut will inform you during the payment process as soon as it verifies you and sends a confirmation email. If you do not see the cashback option during the payment process, the purchase is not eligible for cashback. Eligible purchases for cashback may change from time to time without notice.