If you are using Family Sharing and you are not the Organizer then these articles describe that in more details:
Based on: How to share apps and purchases with your family - Apple Support and How apps, content, and subscriptions from Apple are billed - Apple Support
1. If anybody in the family buys or subscribes to something, Apple first attempts to charge the item to that individual's Apple Account (Apple ID) balance, if any.
2. If a family member does not have enough personal Apple Account balance, any excess will be charged to the Family Organizer's primary payment method (usually a card of some kind). The Organizer's personal balance will not be used for purchases made by other family members. If Apple cannot bill the primary payment method, the Organizer will need to make another payment method the primary method. With Family Sharing the Organizer always has to have at least one functioning payment method.
Also note: "Some purchases, including gifts, can't be billed to Apple ID balance and will be charged to the family organizer's payment method." "Some subscriptions might not be charged to Apple ID balance."
Ref:
- Family purchases and payments - How to share apps and purchases with your family - Apple Support
- How apps, content, and subscriptions from Apple are billed - How apps, content, and subscriptions from Apple are billed - Apple Support
- Check your Apple ID balance - Check your Apple Account balance - Apple Support
- Add a payment method to your Apple ID - Add a payment method to your Apple Account - Apple Support
Adding funds to your Apple ID balance:
- How to redeem your Apple Gift Card, App Store Card, or App Store & iTunes Gift Card - Apple Support
- Add money to your Apple Account balance - Apple Support
Another possibility:
● If an app or feature on your device is not working, not appearing, or is restricted (grayed out), a frequent reason is it may have been disabled using Screen Time, or by a technology administrator if you are using a device owned by an employer or educational institution.
- Read this support article If your Apple ID or other options are greyed out in Settings —> If your Apple Account is grayed out in Settings, or you can't sign out - Apple Support
Tap your Settings app > Screen Time > Content & Privacy Restrictions > scroll to Allow Changes and turn on.
- If the device is managed (check: Settings > General > VPN (or Profiles) & Device Management), contact the technology department of the organization that is doing the managing.
