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This module attempts to address
You'll need to add a field called "Paid in full" to your order entity BEFORE installing this module. The machine name of that field must be "field_paid_in_full" (or you can edit the code in this module to suit your own needs)
This just adds a rule that sets this field when orders are paid in full, and retrofits the field onto old orders with a batch process. The batch process appears at /admin/commerce (you'll see the menu item on that page)