multiple NAS help

Hello forum members,
I have my network setup as follows. I want to all 3 routerboards to authenticate users from central radius server.
How can i accomplish that without bridging the interfaces.
network.jpg

Radius server will have it’s ip, right? If you can ensure that it is reachable/routable from/to any Mikrotik, it will just work.

Radius Server is reachable from all of the mikrotiks. But radius authentication is not working.