Questions How to see who clicked "Approved for Payment" on an AP Bill?
The APInvoice table has a value for Last Modified By which updates when a user clicks the checkbox to approve for payment, but Last Modified could easily be overwritten if the payment type needed to be changed for example.
There's a tab on Bills and Adjustments page named "Approval Details" - did you look there?
You can also look in the EPApproval table. I don't have approvals turned on for payment, but EPApproval stores the Bill Approval prior to releasing.