You have a few options here!
1. If you just need to invoice to go to a specific person, a customer's billing department, for example, then you can edit the customer's financial settings! First you need to set the Invoice Receipt Method to Email, then a new option will appear for you to Email Invoice To: and select one of the customer's employees in the dropdown. This will automatically send an invoice to that person once the order has reached Shipped status.
2. If you need to invoice to send to multiple people at once, you can add a tag to each contact.
To tag a contact, you'll need to visit their profile page, and use the tags menu on the right sidebar to add a tag. Something like "Invoice Email" would be the tag I use. Then, once you have all the contacts tagged, go back in your trigger and select the Tag for "Invoice Email" as the email recipient. By using a trigger, you can designate at which point in the order process the invoice sends out.
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Automatically Emailing Invoices
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