Unfortunately, HIBP only supports a single email address per account, so it's not possible to add a separate billing recipient directly.
If multiple people within your organisation need to receive invoices, receipts, and other account communications, the recommended approach is to create a distribution list or shared mailbox on your side and use that email address for your HIBP account.
You can update your account email address via Dashboard → Subscription → Manage Subscription:
https://haveibeenpwned.com/Dashboard/Redirect/Subscription
Using a shared mailbox or distribution list helps ensure continuity when team members change roles or leave the organisation, while also allowing everyone who needs access to receive billing communications.