In order to send a message to facebook messenger a user must initiate the conversation by sending a message or subscribing to your facebook business page first. Once a user is subscribed to your page you will get a unique
"messenger_id" of the user , this id will be used to communicate further with the user.
We make use of the Same Web-hook & API Structure for all messaging app, so that you can just add few parameters to integrate any messaging channel we support, just replace the below parameters while receiving and sending messages.
Unique ID given by the facebook
User Full Name as updated by their facebook / messenger profile
Sending location but able to receive location from a user