I am having the same issue.  What the QB user is referring to is the "behind-the-scenes" information in QuickBooks, in the data itself.  Say an invoice is created, QuickBooks assigns that entry a specific transaction ID for that transaction only.  It isn't the invoice number or anything you see on the front end.  It's in the programming part of QuickBooks.  For example, say you want to sync data from QuickBooks to another software.  The transaction ID is used to share that particular item, whether it be an invoice, a payment, a new employee, etc.  It tells both software programs that the records are or are not synced, for example.  No two transactions will (and can't) have the same transaction ID.  It's automatically generated in QuickBooks in the back end, never seen on the screen.  We used to run custom reports in QuickBooks desktop to see those transaction ID's.