After issuing a fiscal receipt, the specific invoice can be sent via email to the customer. To send the invoice, go to the Receipts menu in the POS and follow these steps:
1. Select the order for which you want to send the invoice and hold click on it. Then select the Email invoice option.
2. Select the customer or add a new one (from the + button) and push the send button.
In case the customer has an email address saved, the invoice will be sent automatically, by clicking "send email"
In case the customer doesn't have an email address, you can add it here and then press the send button.
If you want to add a new customer, check this article. How can I add a new customer?