Additional details can be added to the final copy of an invoice.
This can be useful if you would like to add details, such as an insurance claim number.
How-to
Add extra client details on an invoice
Navigate to Workspace Settings.
Under Finances, select Invoices.
Scroll down to Invoice Templates, then select the Edit icon.
Under PDF Display, select the Show Extra Client Invoice Details checkbox.
Once you have done this, head to a client's details page. Edit the client's details, and scroll down to Invoicing. Under Extra Client Invoice Details, enter the additional information. Any information added here will be displayed on the final copy of the invoice.
Click Save to confirm the addition to the client's details.