Cal. Code of Civil Procedure § 473.2

(a) A party that was not served with a summons and complaint in accordance with this chapter may file and serve a motion to set aside or vacate the default or default judgment and for leave to defend the action or to move for dismissal. (b) (1) A party moving to set aside or vacate a default or a default judgment pursuant to subdivision (a) shall proffer evidence, through a sworn affidavit or otherwise, that service was not lawfully effected. Proffering evidence that service was not lawfully effected rebuts a presumption of the facts stated in the process server’s return. (2) If a process server files their return before the operative date of this section, the absence of the photograph required by Section 417.10 shall not by itself render the proof of service unlawful or insufficient. (c) In responding to a motion that is filed pursuant to this section and that complies with subdivision (b), the party seeking a default or default judgment has the burden of proving by a preponderance of the evidence that service of the summons and complaint was lawful. (d) In deciding a motion filed pursuant to subdivision (a), the court shall take evidence as to the lawfulness of the service of process and shall not deny a reasonable request by either party to conduct a hearing and permit oral testimony. (e) This section does not limit any other remedies available under law. (f) This section shall become operative on January 1, 2027.