如何使用FedEx Web Services获取标签？

Question

我正在使用我的开发人员凭据进行FedEx Web服务，使用RocketShipIt API，它只是一个XML包装器。

问题是label_img变量一直是空的：

以下是我使用的示例代码：

$shipment = new \RocketShipIt\Shipment('fedex');
$shipment->setParameter('service', 'FEDEX_2_DAY');
$shipment->setParameter('toCompany', 'John Doe');
$shipment->setParameter('toName', 'John Doe');
$shipment->setParameter('toPhone', '1234567891');
$shipment->setParameter('toAddr1', '111 W Legion');
$shipment->setParameter('toCity', 'Whitehall');
$shipment->setParameter('toState', 'MT');
$shipment->setParameter('toCode', '59759');
$shipment->setParameter('toCountry', 'US');
$shipment->setParameter('packagingType', 'FEDEX_ENVELOPE');

$shipment->setParameter('length', '5');
$shipment->setParameter('width', '5');
$shipment->setParameter('height', '5');
$shipment->setParameter('weight','0.1');


$response = $shipment->submitShipment();

echo "<pre>";
print_r($response);
echo "<pre>";

我得到了回应：

Array
(
    [status] => SUCCESS
    [charges] => 17.61
    [trk_main] => 794663231443
    [tracking_detail] => Array
        (
            [id] => 794663231443
            [type] => FEDEX
        )

    [pkgs] => Array
        (
            [0] => Array
                (
                    [pkg_trk_num] => 794663231443
                    [label_fmt] => PNG
                    [label_img] => 
                    [cod_return_label_img] => 
                )

        )

)

我搜索了所有的FedEx和RocketShipIt文档，没有任何运气。我不知道为什么我的label_img为空。也许是因为我使用的是开发者凭证？但是，开发人员测试凭证的想法被滥用了。