i'm new, and i've a problem with webservice.

when i try to retrieve customers filtering by date\_add i get this error:

```
<message><![CDATA[This filter does not exist. Did you mean: "deleted"? The full list is: "id", "id_default_group", "id_lang", "newsletter_date_add", "ip_registration_newsletter", "last_passwd_gen", "secure_key", "deleted", "passwd", "lastname", "firstname", "email", "id_gender", "birthday", "newsletter", "optin", "website", "company", "siret", "ape", "outstanding_allow_amount", "show_public_prices", "id_risk", "max_payment_days", "active", "note", "is_guest", "id_shop", "id_shop_group"]]></message>

```

this is my code:

```
$yesterday = date("Y-m-d H:i:s", time() - 60 * 60 * 24);

$webService = new PrestaShopWebservice(PS_SHOP_PATH, PS_WS_AUTH_KEY, DEBUG);

// Qui imposto le opzion dell'array per il Webservice: in questo caso i clienti e setto che il formato è json
$opt = array( 'resource' => 'customers',
                        'filter[date_add]' => '['.$yesterday.']&date=1',
                        'display'  => 'full',
                        'output_format' => 'JSON'
                        );

// faccio la chiamata
$xml = $webService->get($opt);

```

I'm stuck, I do not know what to do !!! any help is appreciated