Dialogflow Messenger集成的列表模板（V1 API）

I'm developing a Facebook app that utilizes a messenger bot that posts to my dialogflow agent, which then posts to my backend PHP webhook.

The problem is that I can't find correct documentation to post back a list template.

I have this (working) code to send back a button template:

$array = array(
    "source" => $source,
    "speech" => 'test string',
    "data" => [  "facebook" => [
        "attachment" => [
            "type" => "template",
            "payload" => [
                "template_type"=>"button",
                "text"=>"Try the URL button!",
                "buttons"=>[
                  [
                    "type"=>"web_url",
                    "url"=>"https://www.messenger.com/",
                    "title"=>"URL Button",
                    "webview_height_ratio"=>"full"
                  ]
                ]
            ]
        ]

        ]
    ],
    "displayText" => 'xd',
    "contextOut" => array()
);
echo json_encode($array);

To be clear; this code works fine, and I took it from the documentation here: https://developers.facebook.com/docs/messenger-platform/send-messages/template/button

But if I take code from the same source, and adapt it to dialogflow and implement it as show here:

$elementList = array();
foreach ($listings->results as $value) {
    array_push($elementList, [
        "title" => $value->eventname,
        "subtitle"=> $value->description,
        "image_url"=> $value->imageurl,
        "buttons"=>[
            [
            "title"=> "View",
            "type"=>"web_url",
            "url"=>$value->link,
            "messenger_extensions"=> true,
            "webview_height_ratio"=> "tall",
            "fallback_url"=> $value->link
            ]

        ]
    ]);
}



$array = array(
    "source" => $source,
    "data" => [  "facebook" => [
        "attachment" => [
            "type" => "template",
            "payload" => [
                "template_type"=>"list",
                "top_element_style"=>"compact",
                "elements"=> $elementList,
                "buttons"=> [
                    [
                      "title"=> "View More",
                      "type"=> "postback",
                      "payload"=> "payload"            
                    ]
                ]
            ]
        ]

        ]
    ],
    "contextOut" => array()
);
echo json_encode($array);

The array comes out in the format I want it to, and the same format that is shown in the documentation. But when I post that to dialogflow, and I test it within the messenger client; I get a blank response.

Any guidance is appreciated.