Starting February 1, anyone flying within the U.S. without a REAL ID or another approved form of identification will have to pay a $45 non-refundable fee for TSA to verify their identity. REAL ID has technically been required since May, but travelers were only getting warnings until now.

The TSA says the fee is meant to push the remaining travelers to get the upgraded ID. Identity verification isn’t guaranteed, though — and passengers who can’t be verified may be turned away. If approved, the verification lasts for a 10-day travel window.

You can pay the fee online before arriving at the airport, but TSA warns the process can take up to 30 minutes.