3D Secure (3DS) is an additional authorisation for online card payments that helps fight against fraud. If a merchant requests it, you'll receive a push notification asking you to confirm if you're authorising a payment. You will have up to 5 minutes to decide.
If you didn't receive a push notification, you can launch the Revolut Business mobile app and an authorisation prompt will appear there automatically. You must be logged into a Revolut Business mobile app to complete the authorisation. Make sure you have the Revolut Business mobile app installed (black icon) for your Business account and not the personal Revolut app (white icon).
Revolut Business has no control over which merchants require you to go through the 3DS process. If 3DS didn't prompt and your payment got declined, you can add the merchant as trusted and make the payment again: