CXone Data Action JSON mapping failing on nested array

Trying to map a nested array from an external REST call in a Data Action. The response is fine, but the variable mapping fails silently.

"items": [{"id": 1, "name": "test"}]

Mapping response.items[0].id to a string variable returns null. Is the JSONPath syntax different in the DFO integration? Or am I missing a type conversion step?