If you've spent any time around telecom billing systems, you know they're not your typical CRUD app. You've got prepaid balances, real-time charging, usage events flying in every second, and downstream systems that need to know about things right now not in 30 seconds. So when you're wiring up integrations, the question of "do we poll or do we listen?" comes up fast.
how REST APIs and webhooks actually play out in this context, and where each one earns its place.
The Core Difference (Without the Textbook Version)
REST APIs are pull-based. Your system asks: "Hey, what's the current balance for subscriber X?" and the billing system replies. You're in control of when data moves.
Webhooks flip that. The billing system says: "Subscriber X just crossed their data threshold here's the event payload, do something with it." You register a URL, and the billing system pushes to you when something happens.
