Thanks for the comment and great to hear from you. I think you make a couple great points. (1) Measuring the cost per invoice can be a huge challenge; and as you point out, the value in using it for the business case is to understand the potential efficiency gains for a specific department. (2) AP departments need to focus on quality (or what I refer to as accuracy) and seek to improve it since it can be a huge cost driver.

The most important metric for AP is measuring input quality. If input quality improves, AP productivity increases greatly even if AP makes no process or automation changes.

I recently dealt with a firm with 96% of their invoices coming in as electronic structured invoices yet they had, in my opinion, too many people in AP. 18 people spent 100% of their time resolving discrepancies. They knew the causes but did not understand which to fix. A simple analysis identified 3 sources of nearly half of the discrepancies. Fixing those took 3 days and freed up 8 of the 18 people.