Can I filter on specific category items

Hi, Hoping someone can help me. I am trying to populate a secondary drop down based on the choice of another drop down but if I attempt to apply filtering to the specific category I get nothing returned. Am I doing something wrong or is the following even possible?

<?php
include($_SERVER['DOCUMENT_ROOT'].'/perch/runtime.php');
$sectorID = $_POST['sectorID'];

$subSectors = perch_categories([
                'set' => 'sectors',
                'template' =>'ajax-sub-sectors.html',                
                'filter' => [
                    [
                        'filter' => 'catSectorID',
                        'match'  => 'eq',
                        'value'  => $sectorID,
                    ],
                    [
                        'filter' => 'catSubSectorID',
                        'match'  => 'neq',
                        'value'  => 0,
                    ],
                ]             
            ]);            

echo $subSectors;

?>

Many thanks