Domains categorised under Financial Services (i.e banks and financial institutions) are blocked by default for the age group (9-12). I have changed the restriction on your son's profile and he should now be able to access the ANZ app at any time except during Sleep routine.
For your information, you can control which website categories to block/or unblock by logging in to Family Zone web account then search under Cyber Safety>Controls>Categories.
I have checked your account and confirmed that the in-app purchases option is already allowed under the restrictions setting.
Are you able to see the App store at all or does it come up with an error message when you tap on the App store icon?
Try performing a borrow a request on your daughter's phone and assign the device to yourself by:
Opening the Mobile Zone App
Tap: User circle (your daughter's name)
Select: User to borrow to (yourself)
Input: Pin for user
Check whether the App store is unblocked. If the App store works, end the borrow request by reassigning the device to your daughter.
If the problem is still not fixed, please request a callback here and one of our customer support representatives will call you at the scheduled time to go through troubleshooting.