Legal Question in Business Law in California

Hard to say, based on such a limited set of facts. First, if the job you did was one requiring a contractor's license, and your price was over $500, you'll need a license in order to sue. However, when the customer is a friend, maybe a lawsuit should not be the first thought, license or not. How much is involved? What excuses is he giving for not paying? Would negotiation help any? Was he satisfied with the job? Is it something for which you can get a mechanic's lien? Was there a written contract? Need more information.