Building a usage based pricing system is hard!

A billing system with usage based pricing typically consists of Event Sources, UBP Tool, Collection System, and Account State Manager. However, building such a system presents several challenges including scalability, customization, configurability, robustness, and reliability. Keyser Soze refers to the elusive dream of creating an internal UBP tool that can be completely built and forgotten. Some key considerations for designing a usage-based pricing system include idempotency, one-off invoices, customer acquisition initiatives, just in time changes, access control & approvals, account for bugs or outages in event sources, geographic expansion, reporting & projections, and managing the service itself. These challenges require significant investment of time, effort, and funds, making outsourcing internal tooling for pricing a viable option.