Sidou seems like your URL in config.php is http://. Update it to https://.
In any case you should change your DocumentRoot to the public folder or use https://flarum.org/docs/install.html#customizing-paths to remove public from the URL. You'll also need to update the url in config.php to remove the subfolder once that's fixed.
Grammar warrior PS: discussion #9 appears to have multiple typos in its title 😛
