If you are an Independent Trainer, should you list a gym as an additional insured on your liability insurance?

I have my own insurance as a Trainer, however I’ve been asked by a gym to list them as “additional insured” if I work for them as a 1099. I’ve only worked for gyms as an employee and never had to list them on my insurance since they have their own. Don’t all gym have to have insurance themselves? (this is a franchise gym – not a mom/pop shop).