My Credit Card works but it gets declined by Apple ID payment method

From your description the most likely cause is if you are using VPN, or even if you just have a VPN profile installed in Settings/General/VPN & Device Management/VPN.

I’ve already posted the other things to check in this thread, but here they are again:

A “payment declined” or “card declined" message means that the issuer of the credit or debit card you have on file in your iTunes account rejected a charge or account confirmation. It is not an Apple problem; Apple is just passing through the message from your issuer. There are a number of reasons the charge or verification might be declined:

• Apple is not allowed to accept credit or debit cards in your country
• The card is not recognized in your country
• Insufficient balance or account in arrears
• Account suspended for suspected fraud (not necessarily by you)
• Error in card number
• Wrong expiration date
• Wrong security (CVV) code
• Address in your iTunes account does not match exactly the billing address for the card
• If you are trying to add the card to the Apple Wallet the issuer doesn't support the Wallet
• The card was not issued in the region of the iTunes store
• You are connected through a VPN provider that does not terminate near your actual location.

Here is additional information from Apple→If your payment method is declined in the App Store or iTunes Store - Apple Support

Related issues for specific messages:

• If a message says 'billing problem with previous purchase' or 'verification required'
• Your account has been disabled in the App Store and iTunes