In > Settings > Invoice, you could set
1. Invoice number pattern
2. Invoice Template
You could upload the logo, payment information, header and footer to be displayed on the invoice. Clicking on Preview will show you how it looks before Save.
3. Invoice layout
* Duplicate = One A4 contains two A5 invoices
4. Invoice Email Template
Input the subject, then input the content and placeholders in the Text box.
5. Select Contact Method below and save.
6. Enabled Auto Send, invoice will be sent to the customer every time when it is updated.