Hello, this is Ttagkkuk. Thank you for purchasing and listening to my lecture. It would be difficult to create a lecture on implementing payment functionality with Spring Boot right away, so I will share my knowledge in writing. For toy project level payment functionality, I recommend using I'mport. Payment involves integration with an external API, and the success and failure logic after payment authentication is important. Validation during the authentication process should always be implemented on the server. If the amount comparison fails, you should follow the failure logic to restore the product quantity and used coupons, and then go to the order failure page. If the validation passes, you should go to the order success page and be able to cancel the order from the My Page. Order cancellation should also restore the product quantity and used coupons. Payment functionality is important for integration, but validation and recovery logic are key!