Forbidden / Insecure when

Hi.
When I try to grant access to the plugin (I have created my Google Cloud app, etc), I see the window where you can give access to your Google Cloud account, and when I press the “Ok” button, I get a blank window with the “Forbidden” error.
If I try to refrehs page I get 404 Not Found / nginx error.
I know that my hosting provider is really secure so I wrote to them, but, at first intance, I need to know why the app is “insecure” and how to fix it?
I dont have Google Workspace account, just free account.
Thank you.