How to correctly set up a cascade connection?

[DROZD01]

So here's the plan:
Clients => Server A => Server B => Internet

Both servers have public IPs, both are VPS'es
Server A already has Kea set up for handling DHCP on a created virtual TAP, with the subnet of 192.168.30.0/24 (and TAP itself seems to be 192.168.30.1), and Bind9 for DNS.
I set up cascade connection on Server A to Server B, and clients of Server A are visible through "Server Manager" app on Server B (so i assume the link has been established).
I did not set up anything on the Server B yet, other than SoftEther itself. I did create another TAP on it, and manually assigned it 192.168.30.2 address.
Right now i can ping 192.168.30.2 from a client and get a reply, and i can ping 192.168.30.1 for Server B and get a reply, but pinging 192.168.30.2 from Server A does not work.

How do should i set up Server B in order for it to route all external (not the traffic between clients on 192.168.30.0/24) traffic through it's eth0 interface?

[solo]

On B set DisableKernelModeSecureNAT = 1

To block intra-client traffic adapt VPN Gate's packet filtering rules viewtopic.php?f=7&t=68039#p97841

[DROZD01]

On B set DisableKernelModeSecureNAT = 1

And what does this do? I did apply this to the Server B, but no change in behavior occured.

To block intra-client traffic adapt VPN Gate's packet filtering rules viewtopic.php?f=7&t=68039#p97841

I don't need to block connections between clients, I just don't want them to get routed through Server B and back (if it's even something that could happen).

Maybe there's a more in-depth guide for setting up such a config somewhere?