Private network between servers in pool

Hi there
I have migrating from ESXI to xcp and I am stuck at this bit…

In ESXI to create a private network between any vms I just add a second interface… assign them private IPs and off we go. It auto-magically does everything

In XCP i have tried creating private / virtual networks but I cant get any two vms on different server to ping each other.

The will if the vms are on the same server… but not across servers.

What am I missing.

All servers have 1 physical nic to a public IP address.

You can follow the methods they have here

Or the option that I choose is creating a VLAN that for that pool and in the switch that connects them.