Determining Invoice Payments Complete Status via Automation

Hi all. We would like to automatically send out a graduate certificate after a program is complete and the student’s invoice has been paid in full. The only piece that we’re struggling with is automatically identifying when an invoice is complete and all payments on the invoice payment plan for the student have been successfully paid. There is no “paid” status field and I haven’t found a place in the system where a comparison of Invoice amount and Paid amount can be automatically done in order to apply a “Payments Complete” tag or some other indication that can be used within the campaign to identify when the certificate can be sent.

Any suggestions anyone has to help accomplish this would be greatly appreciated. Thanks so much!!