Home assistant can't auth from outside

Hello There,

I just setup home assistant on raspberry pi and can access the web fine via local network.
I have configured home assistant to be accessed from outside with https and duckdns.

When typing the address, it seems to be able to connect to web (it shows the home assistant icon with loading spin), however, when it tries to redirect to
**..../auth/authorize?response_type=code&redirect_uri....** to show login form, it failed with :

This site can’t be reached

I have setup port forwarding of course. It was working before, not sure why it stopped working now.

Any idea where to look?

Thanks a lot!