If you are in business, you need to have a business license issued by your city and collect taxes.
Your business will success or fail based upon your talent as a photographer ... one reason photographer licenses are not an issue ... and it would be far too hard to devise appropriate tests for each kind o shooter. This was tried in California many years ago and the proposed test assumed that all photographers shot portraits and weddings .... it left out all the industrial, scientific, editorial, sports, animal, industrial, medical and the other photographic specialties.