What are the customers expected to do on a payment failure?
For every payment failure and attempts, Zoho Billing will send email to customers on your behalf prompting them to take necessary action.
So, if a payment fails due to insufficient credit, customer can take settle his outstanding balance before the next attempt so that it can succeed. If it fails due to expired card, customer can update their card using the link provided in the email.
You can also edit these email content and inform the customer how to go about the payment failure. Learn how to edit the email content here.