Incorporating Facebook Messenger into Jitterbit App Builder

Instructions

Get an App ID here https://developers.facebook.com/apps
- Free to sign up
Get your Facebook Page ID here https://www.facebook.com/business/help/2814101678867149
- The Page ID is a numeric value, vanity url will not work.
On the Facebook fanpage that is the target for Messenger, go to Settings>MessengerPlatform>WhitelistedDomains.
- This has to be an HTTPS website.
- IP Addresses and local host won't work
- Make sure to click save!

Create a new HTML Template in App Builder and copy in the below code, substituting your App ID and Page ID you got in the above steps.

<script>
  window.fbAsyncInit = function() {
    FB.init({
      appId            : '[AppID]',
      autoLogAppEvents : true,
      xfbml            : true,
      version          : 'v2.11'
    });
  };
  (function(d, s, id){
    var js, fjs = d.getElementsByTagName(s)[0];
    if (d.getElementById(id)) {return;}
    js = d.createElement(s); js.id = id;
    js.src = "https://connect.facebook.net/en_US/sdk.js";
    fjs.parentNode.insertBefore(js, fjs);
  }(document, 'script', 'facebook-jssdk'));
</script>
<div class="fb-customerchat" page_id="[PageId]"></div>

Add the HTML control to the page of your choice. Once loaded it will follow you throughout the app.

Notes

This also works on mobile!
Facebook considers this to be in Beta
The end user will have to login to Facebook to be able to correspond. There is an alternative plugin that will allow just a one way message from the user to the business.
There are a lot of customizations, auto-replies, color, etc. Here is Facebook's documentaion.
The default is for the window to pop up on Desktop. On mobile it is set to be minimized. Desktop can be configured for this same behavior.