The zone for the pool addresses will be the same zone used for the local side of your VPN policy where you changed the address to 0.0.0.0/0. The internet side is usually called untrust.
To clarify: my pool for the vpn is 192.168.12.50-192.168.12.55
My address with the name "VPN" is 192.168.12.0/32
Your address object for the pool then would be 192.168.12.48/29 - this covers from 48-55