When pinging/connecting to external NAT address, IP of the firewall/router was being returned.
Configure a static nat with proxy arp
ssh into firewall
set security nat static rule-set MIPs rule VCD01XZZZ-BBB match destination-address 151.1xx.xx.210 (external)
set security nat static rule-set MIPs rule VCD01XZZZ-BBB then static-nat prefix 10.xxx.103.xxx (internal)
set security nat proxy-arp interface reth1.0 address 151.1xx.xx.210 (external)
set security zones security-zone trust address-book address VCD01XZZZ-BBB 10.xx.103.xxx (internal)
add to a policy via web config to save time.