Test, if the webserver is able to serve any other file from the webroot, i.e. a static index.html with some content, and a phpinfo.php file with no content except <?php phpinfo(); ?> to see if PHP is working and simultaneously getting information about the web server and PHP.
If you mean the octal values representing the permissions for owner, group and world, that might be not enough unless all files and folders through the whole file system hierachy are world readable. Then the running user of the web server shouldn’t matter. If not world readable, then the user/group who owns the file and the webserver’s user/group come into consideration.
However, if static files are found and served by the webserver, it shouldn’t be related to permissions at all. Hence, the question is why PHP files are not found or executed and thats where your provider/hoster comes into play. Compare the requirements of Kirby with what your provider/hoster offers, if that match at all.
