SAP Dunning: Procedures, Levels, and the Dunning Run Process (AR/AP Advanced Part 1)
Book: Financial Accounting in SAP S/4HANA Finance Simplified: Questions & Answers by Narayanan Veeriah | ISBN 978-93-65898-675
Chapter 17 continues AR/AP with the stuff that happens after invoices and payments: dunning, special G/L transactions, interest calculation, and how FI connects to SD and MM. Part 1 (questions 498 through about 523) is all about dunning. And honestly, this is one of the more operationally useful sections in the book.