You have permission issue. According to your current file permission, only file owner can read and write that file, others cannot read. When you go on browser, default www-data
user tries to read that file. And it is not permitted. Make your file 644
or change file owner to www-data
. ``www-data` is the apache user used while you open php files from browser. And more flexible way, use following;
require_once(dirname(__FILE__) . "/includes/public-application-header.php");