While the register that made the sale is still open, anyone allowed to refund can give the money back: it comes out of that same drawer, and the drawer's count at closing tells the truth about it.
Once that session is closed, the drawer has been counted and the day is on the record. The message tells you the sale belongs to a closed session. From that point only the business owner can refund it.
So if a customer comes back the next day with a receipt, the owner does it. Everything else about the refund is the same: the amount, the reason, and the record on the order.