Capstone Two: Rebuilding Billing

1. The Brief

The billing pipeline is a set of scheduled jobs written over four years by people who have left. It produces invoices that are usually right. Finance reconciles by hand every month and found two double-charges and one missed charge last quarter. Replace it. Nothing may be lost, nothing may be charged twice, and billing cannot stop while you do it.

Write your answer before reading on.

This exercise looks like a migration and is not. The migration is the easy half