Credits are granted once, at the moment the referred customer completes their first checkout. At that point the referrer's wallet receives Digital Amount to Referring Customer (note Referral from #<customer>) and the new customer's wallet receives Digital Amount to Referred Customer (note Referral #<referrer>); both get the referral email (these system emails are on by default but can be turned off). Later orders by the same referred customer do not trigger further credits, but a referrer earns again for each new friend who completes a first order.