The Facebook Messenger template allows sending messages via Facebook Messenger. A Facebook developer account is required to use this template. To use this template, the “API Endpoint” needs to be provided. Follow the steps given in this link (https://developers.facebook.com/docs/messenger-platform/getting-started/app-setup) to set up a Facebook app.
Once the app is setup, you will have access to the page access token. Fill in the page access token in the “API Endpoint”. For example, if the page access token is “ACJA456ASDHJADJ456AFS7BA”, then the “API Endpoint” will be “https://graph.facebook.com/v2.6/me/messages?access_token=ACJA456ASDHJADJ456AFS7BA”
It is recommended to set the “Unique Sent Identifier” to the user attribute you use to identify the recipient. You can do this under advanced settings in the “Template Info” tab. For example, if you are using “phone_number” as the recipient attribute in the content tab, you should set the “Unique Sent Identifier” to “phone_number”.
For more information about the Facebook Messenger API visit https://developers.facebook.com/docs/messenger-platform/reference/send-api/#example_request