All customers should be validated periodically to check for errors in their accounts. A good time to do this is just before each billing cycle. To do so:
Go to Utilities: Administration: Billing: Customers: Configure.
Click Validate all Customers.
A report will be generated showing any customer accounts that have errors (e.g., customer has no lists assigned; or no expiration date for credit card).
Click Editto change the customer information.