php soap-多维数组的发送请求

首先，我尝试使用PHPSOAP发送soap请求，服务接受的XML如下所示

<U_MemberReservedTransaction xmlns="http://tempuri.org/">
  <UserID>string</UserID>
  <password>string</password>
  <memberReservedTransactionRequest>
    <memberReservedTransactions>
      <ReservedType>string</ReservedType>
      <Firstname>string</Firstname>
      <Surname>string</Surname>
      <IcNew>string</IcNew>
    </memberReservedTransactions>
    <memberReservedTransactions>
      <ReservedType>string</ReservedType>
      <Firstname>string</Firstname>
      <Surname>string</Surname>
      <IcNew>string</IcNew>
    </memberReservedTransactions>
  </memberReservedTransactionRequest>
</U_MemberReservedTransaction>

)

至于我期望得到的回报是一个多维数组，但我现在关心的是让我的请求被接受

注意：我得到一个500内部服务器错误

请帮助：

$client->callService('U_MemberReservedTransaction', array(
    'UserID'=>'test1',
    'password'=>'password',
    'memberReservedTransactionRequest' => array( 
    'memberReservedTransaction' => array (
     array( 
        'ReservedType'=>'Renew', 
        'Firstname'=>'', 
                'Surname'=>'',
        'IcNew'=>''
            )
         )
     )