function listCustomers() {

    $authtoken = '2f89455f7767e00d28ea38ee0baa7837';

    $Organisation = '37517635';

    $url = ' https://invoice.zoho.com/api/v3/contacts?authtoken='.$authtoken.'&organization_id='.$Organisation;

    $ch = curl_init($url);

    curl_setopt($ch, CURLOPT_VERBOSE, 1);

    curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, FALSE);

    curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, FALSE);

    curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);

    curl_setopt($ch, CURLOPT_POST, TRUE);

    curl_setopt($ch, CURLOPT_HTTPHEADER, array("Content-Type: application/x-www-form-urlencoded"));

    curl_setopt($ch, CURLOPT_POSTFIELDS, "&JSONString=".urlencode(json_encode($jsonData)));

    $result = curl_exec($ch);

    var_dump($result);

    curl_close($ch);

}