After populating a payment journal with open invoices, if the user removes one or more invoices from the journal because they were selected in error, and then forgets to renumber the documents before posting, the number series "last number used" only advances as far as the last number used before the first gap in the document numbers. The next payment journal creates overlapping (duplicate) payment numbers.

The current implementation focuses on avoiding gaps in numbers, but we care more about unique payment numbers. After working with Microsoft support on this for over a month, we gave up and implemented a customization to automatically renumber documents when a document is deleted from the payment journal, because we can't 100% guarantee that a user will never forget to run the renumber command.

There should be a simple and straightforward way to configure the system to avoid duplicate payment numbers without relying on manual intervention by users. In a number series, "last number used" should actually be the last number used, not "the last number used before a gap".