New installed Hassio cant connect to Google "could not reach [test]app"

Hi everyone,
I freshly installed hassio and running into trouble Connecting it to Google home.
Mit HA is accessable via https with ssl certificate from letsencrypt and via dyndns and nginx proxy manager. I can open the home assistant via mobile data…

I followed the manual stets from this article:

Now when i try to add my [test]app into the google home app i See the logiscreen of my HA instance an can log into it, but shortly after Tha i get the error that google home cant reach [test]app…

Can anybody give some advise?
Tried it multiple Times and also deleting the old google Projects and creating New ones…

Its my first time :pleading_face::sweat_smile: