Section 215 Of Part 2. General Procedural Provisions From California Family Law Code >> Division 2. >> Part 2.

. (a) Except as provided in subdivision (b), after entry of a judgment of dissolution of marriage, nullity of marriage, legal separation of the parties, or paternity, or after a permanent order in any other proceeding in which there was at issue the visitation, custody, or support of a child, no modification of the judgment or order, and no subsequent order in the proceedings, is valid unless any prior notice otherwise required to be given to a party to the proceeding is served, in the same manner as the notice is otherwise permitted by law to be served, upon the party. For the purposes of this section, service upon the attorney of record is not sufficient.
  (b) A postjudgment motion to modify a custody, visitation, or child support order may be served on the other party or parties by first-class mail or airmail, postage prepaid, to the persons to be served. For any party served by mail, the proof of service must include an address verification.