Data Action returns undefined for JSON path mapping in Architect

I am building a custom external integration using a Data Action in Architect. The goal is to fetch some metadata from our internal REST API and pass it to the next step in the flow. The HTTP call itself works fine, I can see the 200 OK response in the trace logs, but the output variable is always coming back as undefined.

Here is the JSON configuration for the Data Action:

{
 "request": {
 "method": "GET",
 "url": "https://api.internal.com/v1/customer/{{interaction.customer.id}}"
 },
 "success": {
 "output": {
 "customerTier": "$.data.tier",
 "loyaltyPoints": "$.data.points"
 }
 }
}

The response body from the API looks like this:

{
 "status": "success",
 "data": {
 "tier": "Gold",
 "points": 1250
 }
}

I have tried changing the path to $.data.tier and also just data.tier without the dollar sign. Nothing seems to work. The trace shows the HTTP request completes successfully, but when I try to use {{data.customerTier}} in the next step, it is empty. Is there a specific syntax for JSONPath in Genesys Cloud Data Actions that I am missing? I am using the latest version of the Architect client.