Picture the following topology
{client} [network A] [network B] {internet}
. . . . . . . . . . . . USG 50. . . . . . . . . . . . Sophos UTM. . . . . . . . . . . .
I have a client on network A that needs to get to a particular website on the internet using one of the IPs on the Sophos UTM WAN side.
I have a working tunnel between the two. The UTM is the router for network B and I have a ZyXEL USG 50 acting as the gateway for network A.
I have set up the following rules:

Where CLIENT is 10.10.10.1 and SERVER is 8.8.8.8
Traffic makes its way over the VPN fine. But the SNAT rule isn't applying. The following tcpdump was run on the UTM box. eth1 is my WAN interface:

So the traffic is leaving the WAN interface without the source address being rewritten. I have also tried adding a masquerading rule but this hasnt worked either.
What have i missed?
Thanks
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