See this article: Where do I find the Pre-set Reports?

There are two types of discounts that are reportable:

1. Promo Code Discounts
2. Automatic discounts

Group discounts are reported on the Manage Groups screen.

You can use this screen for your collections report.  This example excludes contact information for privacy reasons. As you can see from the column labels, you have all information necessary to conduct collection efforts by email, phone or postal mail.

Use the Email Wizard to create and send an invoice to all those with a balance due. How do I create and send an invoice?

This report is only available if you're using specific merchant accounts for credit card processing.