Family sharing of Apple Music with my son - nothing will work

My Apple family is me + my son (11 y.o.), so I am the “organizer”.

I have recently changed my Apple Music subscription to a Family subscription, but on his device it says that I have not shared any subscriptions with the family. On my devices, it says that I have done so and that my son has access.

From browsing various forums and threads, I’m aware this is a common problem, but NONE of the suggested fixes have worked. I have ensured that both of our iOS versions are up to date; we have both tried logging out of “Media & Purchases” and logging back in again (including waiting 10+ minutes each time and restarting our devices); and we have triple checked that I do have the correct Apple ID info for both of us.

My son is not able to log out of his Apple ID because he’s not yet 13 and therefore linked me. I have logged out of my Apple ID and back in again, still no success.

At this point I have no idea what to do fix this but it is frustrating that I’m paying for a subscription that we can’t use.