If you want to send the receipt to the customer by email (this also applies to a simplified tax document and invoice payment), select the Other fiscal data button during payment, tick the Digital (email) option and enter the customer's email address.
Then close the bill with the appropriate payment type and the receipt will be sent to the specified email address.
Due to GDPR, email addresses are not saved in the Setup → Contacts section in the web administration. After the payment is completed, the receipt will not be printed but will be sent to the customer to the entered email address. If you are offline, the device will print a physical receipt.