Cannot add payment method

Did you make sure, that your payment method is accepted in your region?

Payment methods that you can use with your Apple ID - Apple Support

Also check the troubleshooting tips in this related article:

If your payment method is declined in the App Store or iTunes Store - Apple Support

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. Some people also get confused about the formatting of the card expiration date information.