Using this endpoint, you can send the invoice to your customer. When an invoice is in the "draft" stage, the system first finalizes it before sending it to the customer. When an invoice is in "Open" stage already, system just send invoice details to the customer. Your customer will get the invoice through email once you send it via this endpoint. This email will include a PDF attachment of the invoice as well as an invoice URL link that will allow your customer to view invoice information and make a payment.