Nextcloud unable to access from reverse VPN

Guys need help,

My snap nextcloud is behind private ISP IP and so is not facing public ip.Thus I have make reverse VPN that is connected to my VPS. I can access other natted port such as SSH from the same machine as nextcloud but when I did the port forward for nextcloud 443 I did not received answer from outside the public IP.

Is there built in firewall in snap or nextcloud that I should check?

perhaps @kyrofa has thoughts on this?

There is no firewall in the snap. By default it binds to port 80 on all interfaces, and 80 and 443 if you enable HTTPS. Have you done that? Or is it only listening on 80, in which case you should forward port 80?