Anyone who flies a drone for commercial purposes anywhere in the United States must have a Part 107 license from the FAA.
You need to be at least 16 years old, be physically and mentally fit to fly a drone, and be able to speak and write English. If you meet these requirements, then you need to pass the 60 question Part 107 exam to get your license.
The Part 107 exam costs roughly $175 to take and it's administered by an FAA authorized center. The testing fee is non-refundable, so make sure you study before taking it. If you fail the exam, you will need to wait 2 full weeks before you can retake it.
The FAA maintains a list of authorized testing facilities.