Thanks for reaching out to us. We do not have the feature of directly blocking a user from joining the network based on the MAC address or kicking out a user that is already connected. We have this in our backlog.
There are a few related features that might help.
Use case 1: Do not allow a device MAC address to join
Solution: Use a Dynamic PSK (DPSK) network and do not provide a DPSK for the MAC in question.
Use case 2: Allow or block traffic from a user based on L3/L4 parameters (source ip/subnet, src port, dest ip/subnet, dest port)
Solution: Setup traffic policy from advanced network settings in the final step of network creation. This feature will be available shortly (~ 5-7 days)