Screen Time Share Across Devices won’t stay on

I am trying to reconfigure my child’s screen time settings after a previous software update erased all of the settings. I want to be able to change settings on my phone and it will mirror to his automatically, as I could before. However, when I click on “share across devices” it will toggle on and then immediately turns back off. Assuming it was a software issue, I just updated his phone to iOS 17.7, mine is iOS 18. The problem is still persisting.