Dialogflow ES Fulfillment Errors (INVALID_ARGUMENT, URL_ERROR, ERROR_OTHER)

[andrewhappstem]

Hi all, I've had success with Dialogflow fulfillment in the past with other projects, but am running into some errors I cannot seem to debug or find elsewhere. When logging the errors, this is what the payload shows:

Dialogflow fulfillment error : Webhook call failed. Error: INVALID_ARGUMENT, State: URL_ERROR, Reason: ERROR_OTHER, HTTP status code: 400.


I have, of course, tested my fulfillment webhook in isolation, and everything seems to work as expected. I've tested the fulfillment request in Postman, and gotten the following result, which seems to match the fulfillment response spec (Note, I actually changed my webhook to only give back `fulfillmentMessages` to attempt to simplify this debugging process):

{
    "fulfillmentMessages": [
        {
            "text": {
                "text": [
                    "This is a sample webhook response"
                ]
            }
        }
    ]
}

 If it helps, here's what the webhook request looks like:

{
  "responseId": "287e9f23-45b0-434a-9dc2-2b179fb71a5c-e9bf988c",
  "queryResult": {
    "queryText": "Read sequence",
    "parameters": {},
    "allRequiredParamsPresent": true,
    "fulfillmentMessages": [
      {
        "text": {
          "text": [
            ""
          ]
        }
      }
    ],
    "outputContexts": [
      {
        "name": "projects/my-project/agent/sessions/e28407c5-4b07-51f7-8bae-41ae3ea1d7db/contexts/store_restocking_event_id",
        "lifespanCount": 5,
        "parameters": {
          "user_id.original": "6659838d-ce64-413d-bb56-f1a2057f5a3d",
          "store_restocking_event_id.original": "26ec5c5b-b352-42ea-9b14-bd8f9a985850",
          "store_restocking_event_id": "26ec5c5b-b352-42ea-9b14-bd8f9a985850",
          "user_id": "6659838d-ce64-413d-bb56-f1a2057f5a3d"
        }
      },
      {
        "name": "projects/my-project/agent/sessions/e28407c5-4b07-51f7-8bae-41ae3ea1d7db/contexts/read_sequence",
        "lifespanCount": 5
      }
    ],
    "intent": {
      "name": "projects/my-project/agent/intents/ea98d2df-939b-4b05-8c39-8c6bbed8df3c",
      "displayName": "Read sequence"
    },
    "intentDetectionConfidence": 1,
    "diagnosticInfo": {
      "webhook_latency_ms": 190
    },
    "languageCode": "en",
    "sentimentAnalysisResult": {
      "queryTextSentiment": {}
    }
  },
  "webhookStatus": {
    "code": 3,
    "message": "Webhook call failed. Error: INVALID_ARGUMENT, State: URL_ERROR, Reason: ERROR_OTHER, HTTP status code: 400."
  }
}

Thanks for the help!