California Code, Business and Professions Code - BPC § 4855.1

Within 30 days of receiving a written or verbal request by the client or their authorized agent for a record of client payments, the licensee manager of the veterinary premises shall provide a record of client payments made to the veterinary premises related to services and treatment provided.  A record of client payments made to the veterinary premises related to services and treatments provided shall be maintained for a minimum of three years after the animal's last visits.