This function is used when the subscriber should receive the invoice themselves, but a copy of the invoice also needs to be sent to another email address, such as an accounting department.
First, you need to create a field for the invoice copy.
Go to account menu in the top right corner, click on 'Fields'.
Click “New field for” and choose “Subscribers”
Short name: Choose one yourself, e.g., “Invoice copy”.
Type: Select “Email”.
Features: Select “Receives a copy when invoicing via email”.
Text for forms and Help text: Optional—fill in as you see fit.
Pres 'Save'
Then, you need to fill out the field for the subscriber under Subscriber -> Edit basic data.
If you need to use different invoice copy addresses per subscription, the field must be created under Products.