How Does Custom Integration Work with CSP State Changes in Oracle Recruiting Cloud?

Summary:

The client has multiple internal assessment and security screening systems that are not listed on the Oracle Cloud Marketplace and are not certified Oracle partners.
We have configured CSP phases and states to represent each assessment trigger point (e.g. Assessment Initiated, Assessment - Medical Initiated, - Psychometric Initiated etc.).
When a recruiter manually moves a candidate to one of these custom CSP states, we want an integration to trigger.

We would like to understand:
What is the correct mechanism to trigger a custom OIC integration on a CSP state change?Has anyone implemented a similar pattern for non-Marketplace / non-certified assessment systems?