To substantiate means to provide evidence to support or prove your medical transaction is for an eligible medical expense.  The IRS requires that you keep copies of your receipts in the event of an audit.

Varipro can auto-substantiate eligible medical expenses for card swipes made at medical providers if the amount matches the copayment of your medical plan and at retail merchants with an Inventory Information Approval System, (IIAS).

Click  here to read complete document. (Adobe reader or compatible required)