Robux purchase error on family sharing account

Hi,

my son is trying to purchase robux using the family sharing account. We have done so multiple times in the past. But it keeps giving an error.

I asked my other son to send the same request to determine if it’s an issue with my account or my other sons and his request came through and was accepted.

i have force closed the app, completed a hard reset on both my phone and my sons iPad as also deleted and reinstalled the app on my sons iPad.

I don’t know what else to do!