Partial success, but:
https://puma.eukhost.com/~secret/checkout_shipping.php produces
Warning: Unknown(): open_basedir restriction in effect. File(/home/secret/public_html/checkout_shipping.php) is not within the allowed path(s): (/home/puma:/usr/lib/php:/usr/local/lib/php:/tmp) in Unknown on line 0
Warning: Unknown(/home/secret/public_html/checkout_shipping.php): failed to open stream: Operation not permitted in Unknown on line 0