Verify Credit Card data is correct. Its often easiest to remove the current card on file and add a new one. (can be the same one or different)
Open invoice and scroll to the bottom to view transaction details. There are several reasons for a failed transaction. Insufficient funds, incorrect card number, wrong zip code or cvc. If information is incorrect, reenter the payment information with the correct information.
If that still doesn't solve the problem, get the member to ask their bank why the charge was declined. Banks typically don't provide much more data than a generic decline to Stripe so not a lot we can do on our end without this additional information unfortunately.