Error: Data structure returned is not convertible in the requested format. Try to call this method with the parameters '&format=original&serialize=1'; you will get the original php data structure serialized. The data structure looks like this: $data = array ( 7 => array ( 0 => array ( 0 => '2014-09-02', 1 => array ( 'count' => 0, 'starred' => 0, ), ), ), );