External API Data Action output shows undefined for nested JSON path

I’m trying to map a nested value from an external API response using the “Call REST API” data action in Architect. The response body contains "user": {"id": 123}, but when I set the output mapping to $.user.id, the output variable comes back as undefined in the success block. Here is the mapping config I’m using:

{"path": "$.user.id", "variable": "agentId"}

The API call returns 200 OK and the raw body looks fine. Why isn’t the JSON path resolving correctly?