Can't seem to update my childs' apple ID to her new email address. Any ideas?

I have a family setup with one parent and two kids.

Kid (12 yrs) now has her own email so we want to change her apple ID to that new email.

I followed Uw Apple ID wijzigen - Apple Support (NL) but get a message: (translated from dutch:)

"Parental consent is required to make this change. An email request will be sent to your Family Head, [MY NAME], who can provide parental consent for this change."

However. I receive no e-mail whatsoever on my parental mailadress. Not in my inbox, nor in spam.

Either way, I can continue, but after I submit the new address, I get the following message:

"The Apple ID cannot be updated for the account at this time."

Email adresses are not being used with other iCloud users.

It's super frustrating. Any ideas on what might be causing this?

Best, Lars