The object record that the administrator should create in the fault path to notify users of an error is Process Exception. A Process Exception is a record thatrepresents an error or exception that occurred during the order lifecycle, such as payment authorization failure, inventory allocation failure, fulfillment location assignment failure, etc. A Process Exception has a lookup relationship to the Order object,and it contains information such as the exception type, status, message, etc. Verified References:https://help.salesforce.com/s/articleView?
id=sf.order_management_process_exception.htm&type=5

To set up a mock payment gateway in a new org, an administrator shouldtake the following steps:
Create a Payment Provider: This is a custom metadata type that defines the configuration and behavior of a payment gateway. A payment provider specifies the name, type, class, and endpoint of the payment gateway.
Create a Named Credential: This is a Salesforce feature that securely stores authentication information for connecting to external services. A named credential specifies the URL, identity type, authentication protocol, and certificate of the payment gateway.
Create a Payment Gateway: This is a custom object that represents an instance of a payment provider. A payment gateway references a payment provider and a named credential, and defines additional settings such as currency, mode, and timeout. References: Salesforce Payments and Order Management, [Named Credentials]

The administrator can use two tools to debug an issue with an Apex trigger: Log Inspector in the Developer Console and Debug Logs in Setup. The Log Inspector is a tool that displays a graphical representation of a debug log, which is a record of database operations, system processes, and errors that occur when executing a transaction or running unit tests. The Log Inspector helps you analyze and troubleshoot your code by highlighting errors, checkpoints, and execution times. The Debug Logs page in Setup lets you monitor and retain debug logs for users, Apex classes, Apex triggers, and Lightning components. You can view, download, or delete debug logs from this page.