At some point NAT66 prefix translation has stopped working on the 1.5 nightly.
Here's a sample config and ip6tables output showing nothing configured based on the config.
fahad@vyos-vps:~$ show interfaces Codes: S - State, L - Link, u - Up, D - Down, A - Admin Down Interface IP Address MAC VRF MTU S/L Description ----------- ----------------------------------------- ----------------- ------- ----- ----- ---------------------------------------------------------------------------------- dum0 100.1.2.3/32 da:f4:74:8c:09:7c default 1500 u/u Dummy interface for DNS eth0 94.250.203.65/23 00:50:56:44:bf:17 default 1500 u/u 2a02:c206:2076:2040:250:56ff:fe44:bf17/64 2a02:c206:2076:2040::1/64 lo 127.0.0.1/8 00:00:00:00:00:00 default 65536 u/u ::1/128 tun100 2001:470:1f12:452::2/64 n/a default 1476 u/u HE.NET IPv6 Tunnel. Routed Prefixes: 2001:470:1f13:452::/64 and 2001:470:ca0e::/48 vti10 10.0.0.2/30 n/a default 1420 u/u vtun20 100.100.0.1/32 n/a default 1500 u/u wg01 172.31.10.1/24 n/a default 1420 u/u Roadwarrior Client WG VPN fd99:d781:643e:8308::1/64 wg10 172.31.250.1/24 n/a default 1420 u/u WG Tunnel to OpenWRT wrt1900acs for ipv6 gateway 2001:470:1f13:452::f:1/64 wg20 192.168.34.1/24 n/a default 1420 u/u WG Tunnel to VyOS-RTR-N1 wg21 192.168.35.1/24 n/a default 1420 u/u WG Tunnel to VyOS-RTR-N2 wg30 2a11:6c7:f01:3fa::2/64 n/a default 1420 u/u fahad@vyos-vps:~$ show config commands | grep nat66 set nat66 destination rule 9001 description 'Wireguard Incoming NAT66 prefix translation' set nat66 destination rule 9001 destination address '2a02:c206:2076:2040::a:0/112' set nat66 destination rule 9001 inbound-interface name 'eth0' set nat66 destination rule 9001 translation address 'fd99:d781:643e:8308::a:0/112' set nat66 source rule 9000 description 'Wireguard Outgoing NAT66 prefix translation' set nat66 source rule 9000 outbound-interface name 'eth0' set nat66 source rule 9000 source prefix 'fd99:d781:643e:8308::/64' set nat66 source rule 9000 translation address '2a02:c206:2076:2040::/64' fahad@vyos-vps:~$ ip6tables -nvL Chain INPUT (policy ACCEPT 0 packets, 0 bytes) pkts bytes target prot opt in out source destination Chain FORWARD (policy ACCEPT 0 packets, 0 bytes) pkts bytes target prot opt in out source destination Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes) pkts bytes target prot opt in out source destination fahad@vyos-vps:~$ ip6tables -t nat -nvL Chain PREROUTING (policy ACCEPT 0 packets, 0 bytes) pkts bytes target prot opt in out source destination Chain INPUT (policy ACCEPT 0 packets, 0 bytes) pkts bytes target prot opt in out source destination Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes) pkts bytes target prot opt in out source destination Chain POSTROUTING (policy ACCEPT 0 packets, 0 bytes) pkts bytes target prot opt in out source destination