Get Units Latest Positions From User Using Remote API on PRO (error 4)

$url = "http://gps.satellite.ge:8026/ajax.html?svc=core/search_item";


$params = array(
    "spec" => array(
        "itemsType"=>"avl_unit",    /* type of object to look for - unit */
        "propName"=>"sys_name",    /* search by name - "sys_name" */
        "propValueMask"=>"*",    /* asterisk means to find units with any names  */
        "sortType"=>""        /* empty value means to sort results by name */
    ),
    "force"=>1,            /* cache is not used */
    "flags"=>1025,            /* object flags to be returned */
    "from"=>0,            /* starting index for returning result */
    "to"=>0                /* return maximum number of objects */
);



$json = json_encode($params);



$ch = curl_init();
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch,CURLOPT_POSTFIELDS,'params='.$json.'&ssid='.$_SESSION['ssid']);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
$result = curl_exec($ch);
$result = json_encode($result);
curl_close($ch);