Developers building ChatGPT apps need to choose a monetization strategy, with external checkout being the recommended method. This approach requires directing users from ChatGPT to a developer-hosted checkout flow on their own site. Currently, this is limited to physical goods, but there are plans to expand to more types of commerce. For select partners, Instant Checkout is available in beta, allowing a smoother payment process directly within ChatGPT. The external checkout process involves several steps. After a user engages with the app and decides to make a purchase, they are redirected to the developer's checkout page where payment details are managed. Key responsibilities lie with the developer, including handling pricing, taxes, and compliance. Once a purchase is confirmed, users can return to ChatGPT to access new features. For Instant Checkout, developers use the `requestCheckout` function to create a checkout session and display payment options. This session must include details like line items, totals, and payment provider info. Developers need to ensure their checkout session payload matches their backend calculations and meets the standards set by the ACP. Error handling is crucial, as issues during payment can arise. The system provides specific error messages, such as payment declines, which are displayed to users during checkout. Developers can also test the payment process using a test mode that simulates transactions without moving real funds, allowing for thorough testing before going live.