Technical stuff alert--this is for system integrators.

To help improve data quality of merchandise and concessions in integrated third party systems, on every order that includes merch or concessions items, those individually sold items will include a [TransactionHash] property. That's easier and more reliable than relying on line item IDs or a compound ID.

You'll see this extra, helpful field in any call that returns customer purchases, like /Customer or /Order/Anonymous

For Salesforce and other CRM integrations, this solves any issues showing some dupe merch or concessions sales for repeat customers.