Let people start a conversation on your website and continue in Messenger. It's easy to set up. Chats started on your website can be continued in the customers' Messenger app, so you never lose connections with your customers. Even those without a Facebook Messenger account can chat with you in guest mode, so you can reach more customers than ever.
You need to update your domain whitelist in your fanpage → Settings → Advanced messaging, then add below domains into your Whitelisted domains section: