Open invoices fall into current, 1–30, 31–60, 61–90 and 90+ days, per customer and in total. The ladder then climbs: a reminder at day 1, a formal reminder plus late fee at day 5, escalation to the corporate contact at day 10, a final notice at day 20, a collection case at day 30. Each rung is recorded against the invoice once, however many times the job runs, and only ever moves forward — recorded being the operative word, because until you configure a relay the step is written as pending and nothing leaves the building.
Late fees can be fixed, a percentage or per-day — each with a grace period and a hard ceiling, and each raised as its own invoice so it can be chased and credited separately. You can rehearse the whole run before anybody is chased, and rehearsing costs less authority than running it. The five rungs themselves are a fixed default: their days and their channels are constants, and there is no screen yet that edits them or varies them by customer.