2. Head to Sales Channels. Under Online Store, click Themes to open the Themes page.
3. Below the Current Theme section, click Customize.
4. You will see a preview of the shop. Click on Theme actions.
5. In the pop-up menu, click Edit code.
6. You will be presented with a number of ".liquid" files. Find the main theme file, usually named theme.liquid, which usually starts with <!doctype html>.
7. Scroll through the code on the right hand side and find the lines of code starting with <body>. For example, the code might start with <body class="template-{{ request.page_type | handle }}">.
8. Paste the Facebook chat plugin settings code into the line below the <body> code.
9. Click Save at the top to complete the operation.
10. Customers can now send messages to you via your website and all messages will appear in the inbox on your business public home page.