A unique identifier that identifies a single line item or multiple line item order.
If an OrderID is used in the request, the OrderLineItemID and ItemID/TransactionID pair are ignored if they are specified in the same request.
Note: Starting in June 2019, eBay will start changing the format of order identifier values. The new format will be a non-parsable string, globally unique across all eBay marketplaces, and consistent for both single line item and multiple line item orders. These order identifiers will be automatically generated after buyer payment, and 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.
For developers and sellers who are already integrated with the Trading API's order management calls, this change shouldn't impact your integration unless you parse the existing order identifiers (e.g., OrderID or OrderLineItemID), or otherwise infer meaning from the format (e.g., differentiating between a single line item order versus a multiple line item order). Because we realize that some integrations may have logic that is dependent upon the identifier format, eBay is rolling out this Trading API change with version control to support a transition period of approximately 9 months before applications must switch to the new format completely.
During the transition period, developers/sellers will use the X-EBAY-API-COMPATIBILITY-LEVEL HTTP header in API calls to control whether the new or old OrderID format is returned in all Trading API call response payloads. The compatibility version is expected to be Version 1113. During the transition period and even after, the new and old OrderID formats will still be supported in all Trading API call request payloads. After the transition period (which will be announced), only the new OrderID format will be returned in all Trading API call response payloads, regardless of the Trading WSDL version used or specified compatibility level.