There is no published minimum volume, and in our experience invoice volume alone is not a reliable qualifier. The business case comes from what manual processing currently costs you: the handling cost per invoice multiplied by annual volume, plus the indirect costs of missed early payment discounts, duplicate payments, compliance exposure, and AP time spent on data entry and exception research.
Volume amplifies those costs, so high-volume organizations with complex supply chains tend to see returns fastest. But the strongest business cases we see combine volume with other conditions: manual-heavy processing, high exception rates, an S/4HANA migration on the roadmap, a merger that left multiple invoice processes running side by side, the loss of internal VIM expertise, or an existing deployment that never delivered the value the organization expected. A short assessment can put real numbers against your current cost per invoice and exception load before you commit to anything, which is a better foundation than any volume threshold.