What is the burden of proving that an hourly rate is unreasonable on its face?

While defendants contend the rate was "unreasonable on its face," presumably meaning the rate is unreasonable as a matter of law, they cite no legal authority in support of this assertion. As the appellants, defendants had the burden to affirmatively demonstrate error. (See Denham v. Superior Court (1970) 2 Cal.3d 557, 564 ["A judgment or order of the lower court are presumed correct. . . ., [and] error must be affirmatively shown"].) Simply stating that an hourly rate is unreasonable on its face, without identifying any supporting legal authority, is not sufficient to demonstrate error.