Hi
I had the same issue and by changing the ZT range to 172.x.x.x I was able to route between the 2 networks.
Before I could ping from the Raspberry both the LAN and ZT network but no routing between them.
So, in your case change the ZT network from 192.168.4.0/24 to anything in 172.x.x.x and setup.
See also: