预填充Paypal计费表单电话字段

我在我的web应用程序中使用Express Checkout PHP-SDK (release 96)。

我正在尝试在Paypal上预填写客户的账单详细信息。

$address                  = new AddressType();
$address->CityName        = strtoupper_tr( $order['invoice']['address']['city'] );
$address->Name            = $order['invoice']['title'];
$address->Street1         = $order['invoice']['address']['address'];
$address->Street2         = $order['invoice']['address']['address-2'];
$address->StateOrProvince = $order['invoice']['address']['province'];
$address->PostalCode      = $order['invoice']['address']['postal-code'];
$address->Country         = 'TR';
$address->Phone           = '5004244244';
...
$set_ec_req_details                 = new SetExpressCheckoutRequestDetailsType();
$set_ec_req_details->BillingAddress = $address;

此代码填充表单，除了电话号码。我发现如果我将国家代码更改为"US"，它也可以工作。

我无法在x.com的论坛或文档中找到任何信息。如果有人告诉我有没有办法做到这一点，我会很感激。