Hello ytdutdvtyfty,
Thank you for using Apple Support Communities.
We understand that you are attempting to add Apple Cash as a payment method, but it is being declined because of a problem. We have a couple of articles that should address this issue.
First, there is this article on adding a payment method. We would recommend reviewing it to make sure you are not overlooking a critical step in the process: Change, add, or remove Apple ID payment methods - Apple Support
Then, if you continue to get the same error, there is this article for a payment method being declined: If your payment method is declined in the App Store or iTunes Store - Apple Support
Best regards.