The Messenger customer chat plugin allows you to integrate your Messenger experience directly into your website. Your customers will be able to interact with your business anytime with the same personalized, rich-media experience they get in Messenger.
To add Facebook Chat:
First, log in to Facebook and go to your Business page on Facebook.
Click Settings in the upper right corner.
Select Messaging from the sidebar menu.
Scroll to Your Messenger URL section and copy the Application ID number.
Go to your SITE123 website.
In the Website Editor, click Settings and select Plugins from the drop-down list.
Click the Manage button.
Click the Add New button and select Add New Plugin.
Type Facebook Customer Chat in the search bar and click Add.
In the Application ID field, enter the number that you previously copied from your Facebook Business page. Insert the code, Enable it, and click Save.
Publish your website to update it with the changes you've made.