How to replace the buttons (attachment) only w/ Slack interactive buttons response : <p>I've managed to create a simple interactive button Slack app using a Google Apps Script (GAS).  </p>

<p>I know how to replace the original message w/ the response, but I would like to replace only the buttons, as demonstrated (but not clearly explained) multiple places in the Slack Interactive Button documentation:<br>
<a href="https://api.slack.com/docs/message-buttons#crafting_your_message" rel="noreferrer">https://api.slack.com/docs/message-buttons#crafting_your_message</a></p>

<p>I'd like to do what's demonstrated here: 
<a href="https://a.slack-edge.com/dcb1/img/api/message_guidelines/Example_6.gif" rel="noreferrer">https://a.slack-edge.com/dcb1/img/api/message_guidelines/Example_6.gif</a></p>

<p>Is this an update of the original message, a replacement of the original message with identical text but different attachment, ...?</p>

<p>My current interactive buttons message code looks like this: </p>

<pre><code>function sendMsgWithButton() {

// slack channel url (where to send the message)
var slackUrl = "https://hooks.slack.com/services/...";

// message text  
var messageData = {
"text": "Here's your interactive buttons message.",
"attachments": [
    {
        "text": "Can you click the button?",
        "fallback": "Sorry, no support for buttons.",
        "callback_id": "ptNotificationButtonResponse",
        "color": "#3AA3E3",
        "attachment_type": "default",
        "actions": [
            {
                "name": "userResponse",
                "text": "OK",
                "style": "primary",
                "type": "button",
                "value": "ok"
            }
                   ]
    }
                ]
}

// format for Slack
var options = {
   'method' : 'post',
   'contentType': 'application/json',
   // Convert the JavaScript object to a JSON string.
   'payload' : JSON.stringify(messageData)
 };    

// post to Slack
UrlFetchApp.fetch(slackUrl, options);
}
</code></pre>

<p>My current action URL code right now looks like this:</p>

<pre><code>function doPost() {

var replyMessage = {"replace_original": true,
                    "response_type": "in_channel",
                    "text": "I see you clicked the button."
                   };

 return ContentService.createTextOutput(JSON.stringify(replyMessage)).setMimeType(ContentService.MimeType.JSON);     
}
</code></pre>

<p>Instead of replacing the entire original message, I'd like to replace just the buttons with something like a checkbox and confirmation message as demonstrated in the gif above.</p>

<p>Thanks!</p>
