Use Free orders (no payment information)

Request 

<?php

require ('PATH_TO_AUTH');

$Order = new stdClass();
$Order->RefNo = NULL;
$Order->Currency = 'usd';
$Order->Country = 'US';
$Order->Language = 'en';
$Order->CustomerIP = '91.220.121.21';
$Order->ExternalReference = NULL;
$Order->Source = NULL;
$Order->Affiliate = new stdClass();
$Order->Affiliate->AffiliateCode = 'Partner123'
$Order->Affiliate->AffiliateSource = 'MobilePlatform'
$Order->CustomerReference = NULL;
$Order->Items = array();
$Order->Items[0] = new stdClass();
$Order->Items[0]->Code = '74B8E17CC0';
$Order->Items[0]->Quantity = 1; 
$Order->Items[0]->PriceOptions = NULL;
$Order->Items[0]->SKU = NULL;
$Order->Items[0]->Price = NULL;
$Order->Items[0]->CrossSell = NULL;
$Order->Items[0]->Trial = false; 
$Order->Items[0]->AdditionalFields = NULL;
$Order->Items[0]->Promotion = NULL;
$Order->BillingDetails = new stdClass();
$Order->BillingDetails->FirstName = 'FirstName';
$Order->BillingDetails->LastName = 'LastName';
$Order->BillingDetails->CountryCode = 'us';
$Order->BillingDetails->State = 'California';
$Order->BillingDetails->City = 'LA';
$Order->BillingDetails->Address1 = 'Address example';
$Order->BillingDetails->Address2 = NULL;
$Order->BillingDetails->Zip = '90210';
$Order->BillingDetails->Email = 'customer@email.com';
$Order->BillingDetails->Phone = NULL;
$Order->BillingDetails->Company = NULL;
$Order->DeliveryDetails = NULL;
$Order->PaymentDetails = new stdClass ();
$Order->PaymentDetails->Type = 'FREE';
$Order->PaymentDetails->Currency = 'usd';
$Order->PaymentDetails->PaymentMethod = new stdClass ();
$Order->PaymentDetails->PaymentMethod->RecurringEnabled = false;
$Order->Promotions = NULL;
$Order->AdditionalFields = NULL;
$Order->LocalTime = NULL;
$Order->GiftDetails = NULL;

try {
    $newOrder = $client->placeOrder($sessionID, $Order);
}
catch (SoapFault $e) {
    echo "newOrder: " . $e->getMessage();
    exit;
}

var_dump("newOrder", $newOrder);