When adding a card to keep on file or processing a payment, your financial institution may require you to verify your account/transaction before processing the transaction.
Please follow the on-screen prompts, as the specific steps to do this vary depending on your bank.
Sometimes, when a payment is initiated by the system (monthly billing, for example), you may need to authorize the payment after the fact. If this occurs, the system will send you an email, but you may also view pending payments in your Account:
In the side menu, click My Account > Payment Verification > Reject/Verify. Follow the on-screen instructions to complete the process.