Unable to fetch Custom objects Audit history via RestAPI

Summary:

We have a requirement to capture the audit history of custom objects using the REST API. To support this, we have enabled auditing for the relevant custom object through Manage Audit Policies.

However, when we attempt to fetch audit history using the API below, we are only receiving records for insert actions, and even those contain only the record name attribute.
But, the Audit History Report displaying the complete audit trail for the same custom object, including updates and deletes.

Could anyone assist us in identifying how to fetch the full audit history—including update actions for all audit enabled fields—via the REST API for custom objects?