A merchant has noticed an error in the checkout.

The controller responsible for handling the /checkout URL is located in Controller/Checkout/Index.php in the Magento.Checkout module1. This controller extends from \Magento\Checkout\Controller\Index\Index, which implements the execute() method that renders the checkout page1.

In the Magento_Checkout module, the responsible controller for the /checkout URL can be found inController/Checkout/Index.php. This controller handles the index action for the checkout process, initiating the checkout page when a customer navigates to /checkout. The organization of controllers in Magento follows a convention where the URL path corresponds to the directory structure within the module, making it easier to locate and understand the functionality associated with specific routes​​.