Why can't the customer scan the QR code on the receipt anymore, even though the date is still valid?
The stated validity of the invoice refers to the date of issue of the invoice and not to the current day.
If the number of permitted scans is set to 3, the customer can scan 3 invoices each day. For example, if they have already scanned 3 invoices from previous days and receive 3 more receipts on the same day, they can scan a total of 6 invoices.