Retrieve Array from Webhook Post

[Jonyskids]

I am trying to pull info from an array from within a webhook response.

The response of the webhook is: (Well, the part that is pertinent.)

"task_result": {

          "image_url": "https://imageThumbnail.png",

          "image_urls": [

                        "https://image/0_0.png",

                        "https://image/0_1.png",

                        "https://image/0_2.png",

                        "https://image/0_3.png"

],

[WebHook-Retrieve].[task_result.image_url] allows me to grab the thumbnail and put the url into a cell.

I believe to pull image 0 from the array and put in a cell I should use:

INDEX([WebHook-Retrieve].[task_result.image_urls], 0)

I get: INDEX has invalid inputs

ref:https://support.google.com/appsheet/answer/12738438?hl=en

Please advise.