Dialogflow ES: No fulfillment messages on detected intent (API)

Whenever I make a query to the Dialogflow ES API to test an intent with a custom event named "TEST", Dialogflow is able to link the event with the correct intent.

However, even though the intent is setup with a specific text response, the text response is not returned in the body.

Here is the request's body I am sending:

{
  "query_input": {
    "event": {
      "name": "TEST",
      "language_code": "en-US"
    }
  }
}

And this is the response I get:

{
    "responseId": "478d7989-931b-46ee-b175-30435409c91b-4ecabd93",
    "queryResult": {
        "queryText": "TEST",
        "action": "TEST",
        "parameters": {},
        "allRequiredParamsPresent": true,
        "intent": {
            "name": "projects/*removed*/agent/intents/*removed*",
            "displayName": "TEST"
        },
        "intentDetectionConfidence": 1,
        "languageCode": "en-us"
    }
}

It correctly identifies the intent, however there is no fulfillment text or fulfillment messages. Here are the settings I have for my intent:

Shouldn't there be a fulfillment response with "This is just a test!" in the response?