How Severe is an HSA Audit?
I had an "audit" of my HSA (and Schedule A) one year. They asked for all documents supporting all entries on Form 8889 and Schedule A. It was a letter request, not an in-person audit.
I sent them copies of forms 5498-SA, 1099-SA and W-2 (code W, Box 12), a spreadsheet reconciling the distributions and copies of the receipts that agreed to the spreadsheet. A few of our providers provide an annual statement (at request). Most pharmacies will produce an annual statement (I get mine from CVS online). The rest, I used the invoice. When I sent it all in, a couple of months or so later I received a letter closing out the audit saying no issues found.
Reference:
https://www.bogleheads.org/forum/viewtopic.php?t=207770#p3187806