A unique identifier for an eBay order. This field can be used to make an 'order-level' update. If an order has multiple line items, and the CompleteSale call is being used to update the status of, or provide feedback for a single line item within the order, the OrderLineItemID field or ItemID/TransactionID pair must be used to identify this order line item instead of the OrderID field. If the order only has one line item, it the OrderID field can be used to make any updates with the CompleteSale call.
OrderID overrides an OrderLineItemID or ItemID/TransactionID pair if these fields are also specified in the same request.
Note: In June 2019, eBay introduced a new order ID format, but allowed developers/sellers to decide whether to immediately adopt the new format, or to continue working with the old format. Users who wanted to adopt the new format, could either use a Trading WSDL Version 1113 (or newer), or they could even use an older Trading WSDL but set the X-EBAY-API-COMPATIBILITY-LEVEL HTTP header value to
1113 in API calls. Beginning in June 2020, only the new order ID format will be returned in response payloads for paid orders, regardless of the WSDL version number or compatibility level.
Note that the unique identifier of a 'non-immediate payment' order will change as it goes from an unpaid order to a paid order. Due to this scenario, all calls that accept Order ID values as filters in the request payload, including the CompleteSale call, will support the identifiers for both unpaid and paid orders. The new order ID format is a non-parsable string, globally unique across all eBay marketplaces, and consistent for both single line item and multiple line item orders. Unlike in the past, instead of just being known and exposed to the seller, these unique order identifiers will also be known and used/referenced by the buyer and eBay customer support.
Sellers can check to see if an order has been paid by looking for a value of 'Complete' in the CheckoutStatus.Status field in the response of GetOrders or GetOrderTransactions call, or in the Status.CompleteStatus field in the response of GetItemTransactions or GetSellerTransactions call. Sellers should not fulfill orders until buyer has made payment.