Yes, additional email addresses can be added before an Invoice is sent to the customer.
Video | Step by Step Instructions
Step by Step Instructions -
1 . On the left main menu > Go to Booking > Select the booking for which you would like to add additional email ids

2. Click on "Generate Invoice" if one is yet to be created or click on "Send Invoice" if the invoice is saved as a draft.

3. A pop-up window will open where additional email ids can be entered separated by a comma.

You can also add additional email on an invoice under the left main menu bar Payments > Invoices > Select the invoice and add additional email ids under the Customer section

Related articles -
How to generate & send an invoice?
How to add company terms & conditions?
Batch Invoicing: Batch multiple bookings from one customer into a single Invoice
FAQs -
How do I know if an invoice is paid?
How do I update the Billing Address on the Invoice?
Can I download & print the invoice?