Is there an obvious syntax error in this short php code?

Hi,

I am using a CMS (moodle) which apparently has a built in function is_enrolled()  to verify that the user is enrolled in the course. The function definition and example is here : Function definition

I am trying to use it but it keeps returning 'not enrolled' when the user is actually enrolled. Since I am not really good at php, i am trying to figure out whether i may have not written this right. The link that the user clicks returns the GET, domain.com/x.php?tomato=2&potato=2

x.php

$courseid = $_GET["tomato"];
$userid = $_GET["potato"];
function isuserenrolled($courseid, $userid) {
	$context = context_course::instance($courseid); 
	return is_enrolled($context, $userid, '', true);
}
if (isuserenrolled($courseid, $userid)) {
	echo 'is enrolled';
}
else {
	echo 'not enrolled';
}

Select allOpen in new window

the $context is a function that is copied straight from here

Help.