I followed all the instructions but when I try to add the created app in my google home app, instead of linking to my HA, it just refreshes the list of existing apps in the google home app.
If have a valid ssl certificate, when I go the my HA https url, I don’t get any errors about it.
Have you confirmed that your HA URL is reachable from outside of your own network; for instance from a cellular data connection or a different location entirely?
Depending on your gateway/routing configuration, port 8123 might be reachable from within your own network but not from the internet.