I followed the L2TPv3 docs. It took a reboot for ipsec to start working, but my br0 link wouldn’t come up:
$ show interfaces bridge
Codes: S - State, L - Link, u - Up, D - Down, A - Admin Down
Interface IP Address S/L Description
--------- ---------- --- -----------
br0 10.99.254.20/24 u/D Vlan 12 Bridge
It was only after applying these additional commands not documented in the guide that my bridge started to function (where eth1 is the interface I want bridged)
set interfaces l2tpv3 l2tpeth0 bridge-group bridge br0
set interfaces ethernet eth1 bridge-group bridge br0