blue iris mobile app

[nomad3]

At my wits end, would appreciate any help.
I am running an ASUS router with Openvpn set. That is working just fine and I can see the connection on router UI.
I am running BI mobile app on my android. From inside my LAN, works just fine.
However, while away from my LAN and with Openvpn running, it will not connect.
Have done most of the settings changes people have recommended on various forums etc. but no joy.
I am a novice so likely something silly and easy I have wrong.
I believe it has to do with how to route the router to the BI server, and I've gone as far as I can on the port forwarding thing. But can't tie it all together.
Would appreciate any assistance