California Code, Insurance Code - INS § 10235.9a

For policies or certificates issued on or after January 1, 2017, that contain an alternate plan of care provision pursuant to Section 10231.3, if an insurer and insured cannot agree on the terms of an alternate plan of care, the insurer shall provide a written explanation to the policyholder or certificate holder as to the specific reason or reasons why the agreement cannot be reached.  The insurer shall provide the written explanation within 60 days of the insurer's determination that an agreement cannot be reached.