nitaaikumar Yernar yes try what @[deleted] just said or what I do is I move all the files and folders one path back so that the forum index.php shows up on the home url as expected. I mean all the files and folders in flarum's public directory into the url root and all the other folders and files outside the public directory to one path back.
clarkwinkelmann Yernar please look in the server log files to find the full error message. Also let us know what webserver software/host you are using (Apache/Nginx?, shared/managed/unmanaged VPS?)
