bitly_v3_clicks returns empty array

Hi,

<?php
include "BitlyPHP-master/bitly.php";
$result = bitly_v3_shorten('http://getbootstrap.com/2.3.2/');
print_r($result);
echo "<html>";
echo "<body>";
echo "<a href='".$result['url'] ."'> click here</a>";
echo "</body>";
echo "</html>";
$clicks = bitly_v3_clicks('19ehkZK');
print_r($clicks);
?>

In this code $clicks returns to be empty. Am i doing something wrong here
