将Nusoap PHP参数发送给SAP

Question

我在执行与SAP的PHP（nusoap）集成时遇到问题，连接响应200 OK但返回NULL值，我认为失败的原因在于我如何传递参数，这是代码：

client = new nusoap_client($wsdl, true);
$client->setCredentials($usuario,$pass);
$client->setEndpoint($endpoint); 
$client->soap_defencoding = 'UTF-8';
$client->http_encoding='gzip,deflate';
$client->namespaces = array('soapenv' => "http://schemas.xmlsoap.org/soap/envelope/", 'tg' => "http://www.rutadeltg.com/xml/tgweb",'asi' => "http://rutadelasi/asi/");
$person = array('CedulaCliente' =>    $cedula,'CanalDistribucion'=>$canal,'TipoPedido'=>$tipopedido);
$result = $client->call('SI_Get_Order', $person, 'urn:VentaDirecta:modelo:sap','http://sap.com/xi/WebService/soap1.1');