Explanation
According to the Platform Events Developer Guide, to debug platform events, a developer needs to include the Apex Code and Workflow log levels in the trace flag entry for the Automated Process entity or the overridden user. The Apex Code log level captures the execution of the Apex trigger that subscribes to the platform event. The Workflow log level captures the execution of the event process or the resumed flow interview that subscribes to the platform event. The other log levels are not relevant for debugging platform events. The Database log level captures database operations, such as DML statements and SOQL queries. The Callout log level captures the details of HTTP requests and responses, such as web service callouts. References: Platform Events Developer Guide, Set Up Debug Logs for Event Subscriptions, Set Up Debug Logging

Explanation
Three ways to implement custom post Order processing are:
* Extend cc_hk_invoice to handle custom business logic post Order processing. This hook allows modifying the invoice data or performing additional actions after an Order is placed. For example, the hook can send an email notification or update a custom field on the invoice record.
* Use cc_hk_Order.placeTarget to define a new Order Confirmation page which executes additional business logic. This hook allows specifying a custom Visualforce page that will be displayed after an Order is placed. The custom page can include additional business logic or user interface elements.
* Use Process Builder to implement business processes that execute when an Order record is created.
Process Builder is a tool that allows creating workflows and actions based on criteria and conditions. For example, Process Builder can create a task, send an email, or update a record whenan Order record is created. Salesforce References: B2B Commerce and D2C Commerce Developer Guide, Hooks, Process Builder