You can change your default email templates to affect future invoice and payment request emails to all clients.
To edit your default email templates, follow the steps below:
1) Open the "Settings" page.
2) Under "Invoices & Payments", click "Email Templates".
3) Edit the email templates as you wish! You can click "Insert Snippets" to add fields which will automatically populate with information later on based on the contact and invoice or payment request you are sending.
4) Click "Save".
What happens now?
Future invoices and payment request emails will automatically take the format of the default you edited in the Setttings.