Routing with Point to Point PPPoE WAN subnet

Mk88_it

Hi Guys, i have the following situation and I don't figure out from a routing problem.

USG Flex 500 H

WAN1 P2 external zone wan vlan835 unassigned ip

PPPoE zone wan with fixed ip given from my isp only for PTP (no navigation) 172.31.x.x/32

Subnet for navigation x.x.23.128/30 , usable x.x.23.129 and .130

I created this Policy route for internet surfing from lan trough public ip .129

Incoming interface LAN - Destination any , next hop WAN PPP, SNAT ip object .129

Devices on this LAN navigate correctly with ip .129 but I tried to setup a connectivity check and it always fail

How I can tell to Zywall use ip .129 and/or .130 ?

Is it possibile by creating a Virtual ip on that interface?

Thank you