I can’t add card to payment method. It says: “ Your payment method was declined. Update it or add a new payment method and try again.” What should I do?

See the Apple Support article(s) below. Link to contact Apple Support in the article. 

Apple ID payment information - If your payment method is declined, or you have a billing issue with a previous purchase in the iTunes Store*

Possible fixes.   Fix ‘Your Payment Method Was Declined’ Error In App Store.  -

                          Payment method declined in iTunes or the App Store.   -

Hi. It depends on the bank. For example, debit cards associated with prepaid accounts won’t be accepted. But if you have a routing and account number, you have a better chance of Apple Wallet accepting that instead. Hope this helps.