How to configure single-port device as a router (lede) with vlan switch

I have a optical modem which connected with a vlan switch GS108E V3 first, then with a ASUS AC68U router for PPoE+DHCP function. Below is the GS108E vlan switch & AC68U configuration:
VLAN1(LAN): 2t 3u 4u 5u 6u 7u 8u
VLAN2 (WAN):1u 2t
PVID: port 1: 2
port 2-8: 1
port 1 connected with Optical Modem
port 2 connected with AC68U (WAN port)

robocfg vlans reset vlan 1 ports "0t 1 2 3 4 5t" vlan 2 ports "0t 5u"

Now I want to replace AC68U with a single-port device which installed Lede. Here is the Lede configuration:
staci IP:
remove “Bridge”
port ->“ eth0"

set as "PPoE"
port ->"eth0.2"

iptables -t nat -I POSTROUTING -o pppoe-WAN -j MASQUERADE

But when I connected cable(GS108E port 2) to this single-port device, it could not have Internet connection.
Does anybody has successful experience on how to configure single-port device with vlan switch ?

Thanks a lot!

Set LAN to eth0.1