The Debt and Invoicing Report can be found in the Revenue and Debt app, which details outstanding and overdue debt. Here you can find the total outstanding debt, average debt age and a graph overviewing outstanding debt for the past 6 months.
The details showing in the Debt Report are all based on the invoices you have sent in Famly and the payments you have added to Famly. The invoices appear in the month they were sent in, not the period they are invoicing for.
You can filter on the left hand side if you are looking for something particular, i.e. only those overdue. You can also sort by the method in which they pay (Famly Pay).