They asked for an accommodation. What does the law require?

The obligation is a process, not an answer, and that is the part employers miss. Government Code section 12940(m) covers the duty to provide reasonable accommodation. Section 12940(n) covers the duty to engage in a timely, good faith interactive process. They are separate, and an employer can comply with the first while violating the second, or be found to have violated the second even where no accommodation would have worked.

The usual error is speed. Somebody asks for a specific thing, the specific thing is not possible, and the answer is no. The statute cares about what happened between the request and the no: whether alternatives were explored, whether the employee was asked what would work, whether anybody went back to them.

Requests also rarely arrive labeled. Nobody files an accommodation request. Somebody mentions surgery in passing, or a manager notices that a person who was fine is struggling. The obligation starts at that conversation, and the manager who had it usually does not know that.

Nor is it a single meeting. It is an ongoing obligation that reopens when circumstances change, when a temporary accommodation stops working, or when the employee comes back with something else. Closing the file too early is a version of the same error as answering too fast.

Documentation is the whole defense. Not a form, but a record of what was discussed, what was considered, what was tried, and why something did not work. The employer with notes usually prevails. The employer relying on memory of a reasonable conversation usually does not.