Google analytics

Hi there, another question from the "grav noob" I'm...
I input all params in the " Google Analytics (gtag.js)" plugin and it seems pages got correct behavior with the script and my personal tag.
But on the other side, when I go on my google analytics page, it doesn't show any access. It was working nice (with a simple page) just before I change to grav.
So I'm wondering where can be the problem and I though about the google file that should be implemented to tell them the site has been accepted. (on my case : googleexxxxxyyyyy.html).
But... where should I put it to ensure it works ? directly on roots (www/grav) ? in the user dir ? in the plugin dir ?