Hello, I'm located in CA. I hired a designer to draw a design for a Jr ADU in my property. We signed a contract for 40 hours of labor, not to exceed 60. The 40 hours were paid in full. The contract also states that if the work exceeded 40 hours, it would be discussed with the customer. The designer/drafter did not discussed with me, and just sent me an invoice for an additional 20 after I had payed 40 hours hours without prior notice. He is now demanding for payment and is telling me he will file a CA Mechanics Lien. Is this legal given that he did not give me the opportunity to authorize more than 40 hours of labor?