how to call the function and send the xml request to soap using php

I am unable to send the xml request data to the soap Function.It returns **SoapFault exception: [S:Server] java.lang.NullPointerException in **. when i call the __getFunctions() method it returns

array(1) { [0]=> string(42) "fundResponse process(fundRequest $request)" } 

My SoapClient Calling code is like this

$xml='<?xml version="1.0" encoding="UTF-8"?>
          <FundGate>
          <direction>request</direction>
          <action>FT</action>
          <terminalId>'.$terminalid.'</terminalId>
          <transaction>
          <pin>'.$password.'</pin>
          <bankCode>'.$bankcode.'</bankCode>
          <amount>'.$amount.'</amount>
          <destination>'.$destination.'</destination>
          <reference>'.$reference.'</reference>
          <endPoint>A</endPoint>
          </transaction>
          </FundGate>';
$client=new SoapClient($url);

    try {

        $response=$client->process("fundRequest",$xml);
     print_r($response);
    }
    catch(SoapFault $e)
    {
        echo $e;

    }

Here transaction is object. I am unable to get the Response. and my wsdl code like this

    <portType name="FundGate">
<operation name="process">
    <input wsam:Action="http://xxxxxx/processRequest" message="tns:process"/>
    <output wsam:Action="http://xxxxxx/processResponse" message="tns:processResponse"/>
</operation>
</portType>
<xs:complexType name="fundRequest">
<xs:sequence>
<xs:element name="direction" type="xs:string" minOccurs="0"/>
<xs:element name="action" type="xs:string"/>
<xs:element name="id" type="xs:string"/>
<xs:element name="terminalId" type="xs:string" minOccurs="0"/>
<xs:element name="terminalCard" type="xs:string" minOccurs="0"/>
<xs:element name="transaction" type="tns:transaction"/>
</xs:sequence>
</xs:complexType>

when i call the __getLastRequest() it returns NULL. i am unable to get the result. Please help me. how to send the xml request to the soapfunction. thanks in advance