Help needed with purchasing apps for child's account

Hi,

As a family we have 3 Meta Quests and four accounts. I am set up as the main account with my three boys having child accounts. 

One of the child accounts is using app sharing to use the apps available from the main account. For another we have had to re-purchase the games on his own account so that he can play them.

Now my other boy has received a meta quest for xmas. I have no issue with approving free apps for his account but for some reason I keep going around in circles when trying to purchase apps and now need some help please.

At first my boy made the requests and I approved them in the app and tried to make a purchase. At this point it actually seemed like it was going to work until my bank declined the payment for fraud purposes. 

Since then I've tried re-doing the same approach, I've tried gifting the game, I've tried doing it on the quest, on the app, and on my Mac, but nothing seems to work. I'm not even getting a declined message from my bank now. I just receive an error message from meta titled "Your request couldn't be processed" following an underlying message that says "There was a problem with this request. We're working on getting it fixed as soon as we can".

Obviously happy to provide the account details etc if that will help but also wondered if there's anything obvious that I should check or do to get the issue resolved?

Thanks

Rob