Architect Data Action returning undefined in success output

Getting undefined for my mapped fields in a Genesys Cloud Data Action success step. The HTTP call works fine, returning 200 with valid JSON. Here’s the mapping config:

{
 "field": "result",
 "value": "$.data.customerName"
}

The response body has the data at the expected path. Checked the debug logs, the payload looks right. Still undefined in the output. Anyone seen this?