易趣交易API返回'ISBN缺少值'错误

I am using eBay Trading API to sell products on eBay.

$service = new Services\TradingService(array(
        'apiVersion' => $config['tradingApiVersion'],
        'sandbox' => $config['sandbox'],
        'siteId' => Constants\SiteIds::GB
});


$request = new Types\AddFixedPriceItemRequestType();
$item = new Types\ItemType();
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But it returns an error "ISBN is missing a value. Enter a value and try again.". How to set this value or EAN with this API ?

The ISBN can be specified in the Item.ProductListingDetails.ISBN field.

$item->ProductListingDetails = new Types\ProductListingDetailsType();
$item->ProductListingDetails->ISBN = '01234567890';