From the support article: Update the birth date associated with your Apple ID - Apple Support
To change a birth date to any age below 13 (age varies by country), you must be a member of a Family Sharing group [ Set up Family Sharing - Apple Support ], and your family organizer must approve the change. After you change a birth date to any age below 13, you can't alter it except by contacting Apple Support --> Contact - Official Apple Support
1. Follow the instructions in the article to update the birth date on an Apple mobile device or on the web.
2. Follow the onscreen steps to send an email request to your family organizer.
3. Your family organizer will get an email with instructions to approve the request.
Read the document for complete details.
Read this document about how to view your current payment types and add Apple ID payment methods on an Apple mobile device, a Mac, or a PC --> Add a payment method to your Apple ID - Apple Support
If an item appears in red then it is no longer working and you either need to replace it or get it working again.
Check this resource about what to do if your payment method is declined in the App Store or iTunes Store. Click here --> If your payment method is declined in the App Store or iTunes Store - Apple Support
- Apple is checking with your financial institution if the payment method is valid and receiving a negative response. Make sure the name and address are entered exactly as it appears on your financial institution bills and that the 3 digit CVV is correct. Check with your financial institution about the status of your card.
- Make sure your payment method is up to date or to try a different one ( If you need to change or update your Apple ID payment method - Apple Support ).
- Make sure this is one of the payment methods that you can use with your account, as listed in this support article: Payment methods that you can use with your Apple ID - Apple Support .
・Unfortunately the payment methods list is somewhat general and does include individual brands of cards (I guess there are too many and are constantly changing).
・Also read any footnotes in the document.
・Finally, note that the document only says which methods _are_ acceptable. Apparently certain types (usually a credit or debit card) _must_ also be present under certain situations such as when a subscription is involved.
If you still have problems, contact official Apple Support. Click here --> Choose your country or region - Official Apple Support Select your country, then a product. If you don't see one that handles your issue then keep experimenting with selections until you reach one that gets you a chat session or a telephone call and get the representative to redirect you.
or:
See a list of Apple phone numbers around the world, in this article --> Contact Apple for support and service - Apple Support