If you want to set multiple email addresses for sending the invoice, follow these steps:
Go to the Clients details (section Clients & Brands) and find the required billing address.
In the Actions menu, click on the edit button.
Enter the required email addresses. Note that addresses need to be separated by a comma.
You can also specify multiple recipients individually before sending the invoice, the choice is yours. What's more, you can now effortlessly edit the email body before dispatching the invoice.