On a customer's profile, under Activity > Payments, you'll now find an option to send a credit note to a customer in the form of a pdf. This pdf can also be downloaded on your end.
In addition, its worth noting that the moment you issue a refund in credits to a customer's account, they'll get an email notification like this one.
However, if they need a break down of this refund in the form of a pdf like this one, click that dropdown menu pictured above and choose send/download receipt.
