https://secure.server.name/fbpagemessenger
/How to add facebook page messenger to your website
To setup FB Messenger SDK:
For Facebook Page Admins, the Page settings also provides an easy setup tool for customizing your Chat Plugin. To use the setup tool, do the following...
Go to your Facebook Page > Page Settings > Messaging
In the 'Add Messenger to your website' section, click the 'Get Started' Button.
The setup tool provides a simple UI for customizing the greeting message, theme color, displayed response time, and setting the whitelisted domains for the plugin.
Option 1.
Simply copy and paste the Code Snippet into your admin site "Footer Code" (Messenger will appear for all your website pages) accordingly...
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Go Settings > SEO > Footer Code
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Click "Save", then click "Publish", Done.
Option 2.
We recommend placing the code after the opening <body> tag on pages where you want the plugin to appear. (Messenger will only appear on page that inserted with this code.)
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Go "Pages" > At the left panel look for "SEO Settings" > At "FOOTER CODE" > Paste the "Code Snippet" you copy earlier to the column.
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Click "Publish", Done.
JAVASCRIPT: Below codes are only sample, please get the Code from your Facebook Page accordingly.