Use the Manage Orders feature in Seller Central to see whether the order is valid. You can search by customer e-mail address or order ID. It may be the case that the order has not yet cleared the Amazon.co.jp payment system. In these cases, the search results will indicate that the order is still pending. You should not act on an order while it is still in a pending state. Wait for the order to be posted to your order report or encourage the customer to contact Amazon.co.jp customer service.