FYI Notification for Invoice -- Possible Email Address From Payload

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I am trying to create an FYI notification if an invoice is flagged as "urgent". It was suggested that we could possibly use "Email Address from Payload." I am trying to find documentation on how to use that feature and cannot. Does anyone have any ideas on how it code what emails to use?

 

However, I am not thinking that will resolve the issue as these e mails should only go to invoices in a certain criteria. Any ideas would be helpful.