Changing Invoice destination

[Ghian]

Certain companies have different departments. In this case, there is a gentleman who bought our product in his name for the company, so his account is set up on WHMCS, he now receives all emails and invoices. How does one set that the invoices get sent to a separate email? Like the accounts department. 

I see there is a tab where you can add a sub contact in the contact itself but i do not know how to use it. Would that be the solution?