GetExternalContactAction returning null despite valid JSON response

Architect & Flows
1

I am trying to use the GetExternalContactAction in Architect to look up a customer by their phone number. The external API returns a valid JSON object with the customer details. However, the action in Architect seems to be failing silently and returning null values for the contact attributes.

Here is the JSON response from my endpoint:

{
 "customerId": "12345",
 "name": "John Doe"
}

I have mapped the response fields correctly in the Data Action configuration. The HTTP status code is 200. Why is the data not populating in the flow?