Section 10 — [Application Development] - Order Workflow Processing - Phase 1 https://github.com/vinsguru/data-oriented-programming-course/blob/main/02-order-processing-workflow/01-order-processing-system-phase-1.md https://github.com/vinsguru/data-oriented-programming-course/blob/main/02-order-processing-workflow/04-external-services.md