HA App no connection from vpn or from internal IP

Hello everybody,

Unfortunately, I can’t manage to use the app both on the go and at home. I have a https connection with duckdns and everything works perfectly from the outside. However, as soon as I am in my own network or open a VPN tunnel from the outside with a vpn app, the app does not come to the GUI / HA. Strangely enough, it works with a browser without any problems (only via the internal IP). Only the app has problems with it. However, I cannot access my external duck.dns address internally either. Can someone tell me where I have to put something? Sorry for the noob question…

Thanks a lot