If a customer uses a credit card online but their payment fails, you can enable an automated email notification to be sent to customer with detailed info on their failed payment.
To enable this feature, go to Settings>Advanced
At the bottom of the page, you'll notice a checkbox similar to the image below. If this option is checked, customers will be sent an email outlining their payment has failed & should be removed from their pending transactions from their bank in a couple of days.
