TL;DR — SaaS Billing Platform

Design a SaaS billing platform similar to Stripe Billing that manages subscriptions, usage-based metering, invoice generation, and payment collection for B2B software companies. The system must handle complex pricing models (per-seat, usage-based, tiered, hybrid), proration when plans change mid-cycle, and automated dunning for failed payments. Key features: Create and manage subscriptions with multiple pricing tiers. Support pricing models: flat-rate, per-seat, usage-based, tiered, and hybrid.