Family Sharing: Changing Screen Time Passcode Doesn't Work

Hi there. I have my son's iPhone on Family Sharing and I turned on screen time and added some restrictions. My son has figured out the passcode and now when I change it, it does nothing. He can continue using the old one he figured out. Just to be clear I have gone into Settings, Screen Time, Chosen his name, Clicked on Change Screen Time Passcode on my phone and nothing happens. Please help.