One Sale Case Study # 03: Payment Tracking & Completed Order Review

Documents the deferred B2B payment system where orders are placed on credit and settled later. Covers the order-level payment state machine (Unpaid, Partially Paid, Paid, Overdue, Disputed), per-customer balance summaries with credit limit monitoring, manual payment recording with oldest-first allocation logic, an immutable payment audit trail with reversal entries, and automated overdue alerts that turn collection follow-up into a structured daily workflow rather than a memory-dependent task.