How to C# Soap Request Convert to PHP Code?

I'm trying to integrate SOAP with PHP, but the example given is C #.

I've been trying for a long time, but I guess I couldn't send the parameters correctly.

WSDL Address : https://betatest.elogo.com.tr/webservice/PostBoxService.svc?singlewsdl

Example c# code;

using (PostBoxService.PostBoxServiceClient svc = new PostBoxService.PostBoxServiceClient()) { 
    PostBoxService.LoginType login = new PostBoxService.LoginType();
    login.userName = “test”;
    login.passWord = “test”; 
    
    string sessionId;
        if (svc.Login(login, out sessionId)) { 
        }
}

Example SOAP Request

<soapenv:Envelope
    xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/"
    xmlns:tem="http://tempuri.org/"
    xmlns:efat="http://schemas.datacontract.org/2004/07/eFaturaWebService">
    <soapenv:Header/>
    <soapenv:Body>
        <tem:Login>
            <tem:login>
                <efat:appStr></efat:appStr>
                <efat:passWord>XXXXX</efat:passWord>
                <efat:source></efat:source>
                <efat:userName>XXXXX</efat:userName>
                <efat:version></efat:version>
            </tem:login>
        </tem:Login>
    </soapenv:Body>
</soapenv:Envelope>

I m PHP code;

                $data = array(
                    'login' => array(
                        'userName'=>self::username,
                        'password'=>self::password
                    )
                );
                $client = new SoapClient(self::url,$client_params);
                $client->Login($data);

It shows the following error in PHP code;

[previous:Exception:private] =>
    [faultstring] => String reference not set to an instance of a String.
Parameter name: s
    [faultcode] => a:InternalServiceFault
    [detail] => stdClass Object
        (
            [ExceptionDetail] => stdClass Object
                (
                    [HelpLink] =>
                    [InnerException] =>
                    [Message] => String reference not set to an instance of a String.
Parameter name: s
                    [StackTrace] =>    at System.Text.Encoding.GetBytes(String s)
   at CommonLib.Helper.HelperLib.ComputeMd5Hash(String input)
   at CommonLib.Documents.LoginLogout.Login(LoginType login, String& sessionID)
   at SyncInvokeLogin(Object , Object[] , Object[] )
   at System.ServiceModel.Dispatcher.SyncMethodInvoker.Invoke(Object instance, Object[] inputs, Object[]& outputs)
   at System.ServiceModel.Dispatcher.DispatchOperationRuntime.InvokeBegin(MessageRpc& rpc)
   at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage5(MessageRpc& rpc)
   at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage11(MessageRpc& rpc)
   at System.ServiceModel.Dispatcher.MessageRpc.Process(Boolean isOperationContextSet)
                    [Type] => System.ArgumentNullException
                )

        )

Thank you very much for your help.