Cannot block flows with BGP FlowSpec

Hello team, In my lab setup I have configured a BIRD v2.0.1 VM to peer with an ExaBGP VM via eBGP. I'm using ExaBGP to send FlowSpec rules to BIRD. BIRD correctly lists the received rules when running 'show route table flowtab4' but the respective flows are not affected (i.e. drop traffic to a destination prefix). Is this because of a configuration issue on my side or BIRD does not implement the required FlowSpec actions? Thank you in advance! Best regards, Giorgos