tl;dr
Autonomous invoice processing is the end-to-end handling of an invoice, receipt, data extraction, coding, matching against a purchase order or receipt, routing for approval, and posting, carried out by AI rather than a person moving the invoice through each stage manually.
The difference from ordinary invoice-processing software is what happens when something doesn't fit the pattern: a new vendor, a missing PO number, a line item that doesn't match. Autonomous processing investigates the exception and resolves it, rather than stopping and handing it to a person to sort out later.
See how this works in Light's Workflows.
