If I need to pay for a medical expense and my account does not have enough money to cover it, what happens?

You can pay for it with other funds and then reimburse yourself when the money is available in the HSA account. If an unexpected qualified medical expense comes up, you can deposit additional money in the HSA to cover it, as long as it does not exceed the IRS maximum. You do not have to use the money in your HSA account if you don’t want to.