The text discusses the critical importance of building idempotency into payment and billing applications, particularly in distributed systems, to ensure data correctness and avoid errors like duplicate payments. Idempotency, a property that allows operations to be applied multiple times without changing the result, is essential for managing concurrency in distributed systems where multiple nodes may perform the same operations simultaneously. The text explores methods to implement idempotency, such as using unique transaction IDs instead of timestamps, which can be unreliable in highly concurrent environments. The example of Shipt, a grocery e-commerce company, is used to illustrate how they built a payment system using CockroachDB to achieve atomicity, consistency, isolation, and durability (ACID) while maintaining idempotency. Shipt's system design includes a database schema with regional tables for payments and idempotency tokens, which help manage the data's correctness and prevent transaction duplication. Organizations increasingly turn to solutions like CockroachDB to build scalable payment systems that handle financial transactions accurately and efficiently.