Hi everyone!

I configured my TP-Link VPN Router model ER7206 like this guide of the link below.
https://www.tp-link.com/jp/support/faq/2158/

My router is put behind an ISP modem which run in bridge mode and use PPPOE for access internet.

Everything is configured exactly like the guide and the router can be also accessed internet but L2TP VPN Server on the router is not working.

I don't know that it's neccessary to configure something such as open vpn port in ISP modem or not

Please give me some advice to fix this issue

Thank you!