Even when you swipe the card, the plan provider can request additional documentation to validate the charge is qualified.

Most plans will ask for documentation on the purchase to validate that they are qualified because they want to make sure their plan remains in good standing and qualified.

So there is a pretty good chance that it is caught, unless you plan on outright lying to them. Then that's entirely different ballgame...

Unless they are a dependent under your plan, it would be a non-qualified distribution and would come with taxes and penalties.