Why can’t I pay for my Apple Music ?

Review this document about what to do "If your payment method is declined in the App Store or iTunes Store" Click here --> https://support.apple.com/HT203005 It mostly just suggests you make sure your payment method is up to date or to try a different one. Apple is probably just checking with the system linking to your financial institution and asking if the payment method is valid. The system is providing 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 this is a payment method that you can use with your Apple ID; click here --> https://support.apple.com/HT202631 For most people this means a card from the same country as the store you are using.

If you still have problems Click here --> https://support.apple.com/choose-country-region/ 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:

Contact Apple for support and service --> "See a list of Apple phone numbers around the world." - https://support.apple.com/HT201232

'If you can't remove your last payment method or use no payment method with your Apple ID' click here --> https://support.apple.com/HT203905