Try these commands
set interfaces pppoe pppoe0 authentication password xxxxxx
set interfaces pppoe pppoe0 authentication username xxxxxx
set interfaces pppoe pppoe0 dhcpv6-options pd 0 interface eth1 address ‘1’
set interfaces pppoe pppoe0 dhcpv6-options pd 0 interface eth1 sla-id ‘0’
set interfaces pppoe pppoe0 ip adjust-mss ‘clamp-mss-to-pmtu’
set interfaces pppoe pppoe0 ipv6 address autoconf
set interfaces pppoe pppoe0 ipv6 adjust-mss ‘clamp-mss-to-pmtu’
set interfaces pppoe pppoe0 source-interface ‘eth0’
set nat source rule 100 outbound-interface ‘pppoe0’
set service router-advert interface eth1 name-server ‘xxxx:xxxx::1111’
set service router-advert interface eth1 prefix ::/64 valid-lifetime ‘172800’
Eth0 is wan,Eth1 is lan in this case