How to talk to family about medical transition?

I’m 19 FTM and have been out for about 5 years. I’ve been wanting to medically transition for a very long time but my parents aren’t in agreement. They’ve been mostly supportive throughout my social transition but still don’t believe this will last and are convinced I will regret hormones and surgery. Since they fund my insurance and medical bills I can’t do anything without their support, but the dysphoria is getting worse by the day and severely impacting my life and mental health. Any suggestions on how to have this conversation/explain to them?