Agent Scripting API 400 Error on ServiceNow Data Action Trigger

Could someone clarify why the Genesys Cloud Agent Scripting API is returning a 400 Bad Request when invoking a Data Action to create a ServiceNow incident? The payload validates correctly in Postman against the ServiceNow REST endpoint, but fails within the Architect flow script step.

{
 "event": "script_trigger",
 "payload": {
 "short_description": "Escalation from Agent Script",
 "category": "digital",
 "assignment_group": "support_tier2"
 }
}

The error response indicates a schema mismatch, yet the fields match the ServiceNow incident table structure exactly. Any insights on the expected JSON structure for this specific integration?