无法弄清楚如何调用WSDL服务的函数

Question

最近我得到了一个项目，并提供了一个没有文档的WSDL API。我一直试图计算如何将参数传递给位于此处的WSDL服务：http://www.lme4me.com/webapp/pickupRequest2/services/PickupRequestMethodsV2/wsdl/PickupRequestMethods.wsdl

$this->client = new SoapClient('http://www.lme4me.com/webapp/pickupRequest2/services/PickupRequestMethodsV2/wsdl/PickupRequestMethods.wsdl',
        [
            'trace' => 1,
            'use' => SOAP_LITERAL
        ]
    );

 $data = [
            'PickupHeader' => [
                'shipperPhone' => '0507878328',
                'customerNum' => '1231231231',
                'shipCompany' => 'Optimum7',
                'shipAddress' => '141 Grand Avenue',
                'shipCity' => 'Miami',
                'shipState' => 'FL',
                'shipZip' => '33133',
                'pickDate' => '20/07/2016',
                'pickTime' => '13:00',
                'dockCloseTime' => '13:00',
                'paymentTerms' => 'P',
                'specialInstructions' => 'Test API Usage! Test Pickup',
                'shipmentDetails' => [
                    'unitType' => 'PKG',
                    'units' => '3',
                    'weight' => '44',
                    'consigneeName' => $order->ShipCompanyName,
                    'destCity' => $order->ShipCity,
                    'destState' => $order->ShipState,
                ]
            ],
        ];
        $soapCall = $this->client->RequestPickup_v2($data);

此调用始终返回内部服务器错误。如何通过查看wsdl链接来了解我应该发送什么参数？