Been trying for years and never succeed hosting anything to external IPs. Right now I'm trying to setup a Vaultwarden server on Synology NAS. I have DDNS setup and port forward with reverse proxy setup correctly. However only LAN connection works.

I have AT&T provided BGW320 fiber modem/wifi AP passthrough to Asus RT-AX86U on latest merlin.

Not sure if this is a forwarding issue or firewall or modem to Asus AP passthrough. I have no issue with day to day web browsing and gaming. Services I have working is Openvpn with asus provided ddns on router. Synology quickconnect features also works. Firewall and AIprotect on Asus router are set to OFF as diagnosing the issue.

Anything else I tried hosting with raspberry pi all failed for possible same reason.

It looks like I am missing something there if someone could help pointing it out will be really appreciated.