Xkyer I think that's a bug in Flarum. Flarum generates the canonical meta tag on the page but doesn't add the ending slash for the homepage. This probably doesn't trigger any warning in search engines when Flarum is installed in the root folder because the ending slash is automatically assumed present by any URL parser. But for subfolder installations Flarum is supposed to add the ending slash in the meta tag since it's required for subfolder installations (only the Flarum homepage needs the ending slash, not the other pages added by Flarum or extensions) but it's apparently not doing it. I see the same problem on one of my test websites right now.
