To enable anti-fraud you will first need to create a new anti-fraud connection which can be completed via the dashboard by heading to Connections -> Catalog.
On this page, scroll down to the bottom to explore the available anti-fraud services.
Once configured and activated you can create a new card transactions flow rule with an anti-fraud decision as its condition.
Multiple anti-fraud services
Only one anti-fraud service can be active at any time, but multiple can be configured. This will allow you to migrate your active rules to use scores or decisions from the new service before switching off your old service.