Data Action returning undefined for nested JSON path

Architect & Flows
1

The HTTP POST data action succeeds with 200 OK, but the mapped output field is always undefined. The response payload has a nested structure. I’m using $.data.items[0].id in the mapping config. Standard JSONPath works in external validators, so the syntax feels right. The debug logs show the raw body is populated. Am I missing a type coercion step in the action config? Here’s the mapping snippet:

{
 "output": {
 "targetField": "$.data.items[0].id"
 }
}

The variable stays empty downstream.