The buyer has paid for an item, but the item has not been received within the expected delivery window.
In the case of an item that has not been received by the buyer within the expected delivery window, the buyer has the option of opening up an Item Not Received (INR) Inquiry. If the seller does not address the INR inquiry and the buyer never receives the item, the buyer will escalate the INR inquiry into a case, and eBay will automatically refund the buyer and bill the seller to recoup that money if the buyer wins the case. The Post-Order API provides a programmatic way to submit and handle INR inquiries.
Refer to Handling order inquiries for more information.