Hi again.
My fault. They changed where to find this in a pretty recent iOS update. This should be the correct place to find it:
- Open the "Settings app"
- Tap the first one at the top of the list, called "Your Name, Apple-ID, iCloud, medias and purchases" (with "Your Name" replaced with your actual name)
- Click the third option called "Payment and delivery"
Here you should be able to change your payment method, which is what is causing your verification problem. However, if you can't change it, it could be because a parent or administator in you iCloud family has set it so that it always uses their payment method. If that's the case, you'd have to ask them to turn off the setting that "forces" all family members to use their payment method.
Tell me how it goes and feel free to ask if you have any more questions.
// Gustav