Knock, a notifications-as-a-service platform, implemented a new usage-based billing system in partnership with Orb, which they selected after evaluating various alternatives. The billing system consists of three integrated components: Knock's application system, Orb as the usage-based billing provider, and payment processors like Stripe or Bill.com. Knock synchronizes customer and subscription data, while Orb manages subscription details, meters usage, and generates invoices, and payment processors handle payment information. The integration required custom solutions for billing management, such as capturing payment details using Stripe Elements and managing plan upgrades and downgrades. Knock faced challenges like retrying usage reporting, migrating customers to new pricing models, and handling complex Enterprise plan pricing. Despite trade-offs, the decision to use Orb allowed Knock to focus on core business functions, leveraging Orb's flexible pricing models and robust billing infrastructure, which helped streamline their billing system without getting entangled in complex billing details.