Magento SOAP order failes with message "birthday is required" - php

Question

I use this code to create an order through the magento (1.9) soap api v2.
The problem is, that I have to do this for a site, where the dob (day of birth) is a required field. Therefor I do get an error message - on that site - "birthday is required".
Do anybody know how to solve that problem (without disabling the dob as required field)?
$storeId = '1';
$quoteId = $client->shoppingCartCreate($session,$storeId);
echo "<br>Quote ID : " . $quoteId;
/* Set cart customer */
$guest = true;
if ($guest)
{
$customerData = array(
"firstname" => "testFirstname",
"lastname" => "testLastName",
"email" => "testEmail#mail.com",
"mode" => "guest",
"website_id" => "1"
);
}
else
{
$customer = array(
"customer_id" => '69301',
"website_id" => "1",
"group_id" => "1",
"store_id" => "1",
"mode" => "customer",
);
}
//Set cart customer (assign customer to quote)
$resultCustomerSet = $client->shoppingCartCustomerSet($session, $quoteId, $customerData,$storeId);
echo "<br>Set Customer: ";
var_dump($resultCustomerSet); //Set customer
/* Set customer addresses Shipping and Billing */
$addresses = array(
array(
"mode" => "shipping",
"firstname" => "Ahsan",
"lastname" => "testLastname",
"company" => "testCompany",
"street" => "testStreet",
"city" => "Karachi",
"region" => "Sindh",
"postcode" => "7502",
"country_id" => "PK",
"telephone" => "0123456789",
"fax" => "0123456789",
"is_default_shipping" => 0,
"is_default_billing" => 0
),
array(
"mode" => "billing",
"firstname" => "Ahsan",
"lastname" => "testLastname",
"company" => "testCompany",
"street" => "testStreet",
"city" => "Karachi",
"region" => "Sindh",
"postcode" => "7502",
"country_id" => "PK",
"telephone" => "0123456789",
"fax" => "0123456789",
"is_default_shipping" => 0,
"is_default_billing" => 0
)
);
//Set cart customer address
$resultCustomerAddress = $client->shoppingCartCustomerAddresses($session, $quoteId, $addresses,$storeId);
echo "<br>Set Customer Address: ";
var_dump($resultCustomerAddress); //Set customer addresses
/* Add products to cart */
$product = array(
'product_id' => '905',
// 'sku' => 'simple_product',
'qty' => '1',
'options' => null,
'bundle_option' => null,
'bundle_option_qty' => null,
'links' => null);
$product2 = array(
'product_id' => '904',
// 'sku' => 'simple_product',
'qty' => '2',
'options' => null,
'bundle_option' => null,
'bundle_option_qty' => null,
'links' => null);
$addToCart = $client->shoppingCartProductAdd($session, $quoteId, array($product,$product2),$storeId);
echo "<br>Add to Cart: ";
var_dump($addToCart);
/* Set payment method */
$responsePayment = $client->shoppingCartPaymentMethod($session, $quoteId, array(
'method' => 'cashondelivery',
),$storeId);
echo "<br>Set Payment method: ";
var_dump($responsePayment);
/* Set shipping method */
$setShipping = $client->shoppingCartShippingMethod($session, $quoteId, 'flatrate_flatrate',$storeId);
echo "<br>Set Shipping method: ";
var_dump($setShipping);
/* Set Discount Code */
try
{
$result = $client->shoppingCartCouponAdd($session, $quoteId, 'test123',$storeId);
echo "<br>Apply discount code: ";
var_dump($result);
}
catch(Exception $ex)
{
echo "<br>Discount code Failed: " . $ex->getMessage();
die();
}
$orderId = $client->shoppingCartOrder($session, $quoteId, $storeId, null);
echo "<br>Placed Order: ";
var_dump($orderId);