My River Island
We’re not able to specify why card payments fail as the payment process involves both our systems and your bank’s.
In the first instance you should double check you've entered all the details correctly, that you are using a card which has not expired, and that your billing address has been entered at checkout exactly as it appears on your bank statement. If your billing address is incorrect it will cause your payment to fail - this is a security measure banks put in place to protect your security.
If you wish to try an alternative card for payment, you'll find details of all the ways you can pay in the How can I pay on your site section of our FAQs.