Copied from https://developers.facebook.com/docs/messenger-platform/guides/quick-start. For backup and reference purpose only
This example project creates a Facebook Messenger bot, completely
mirroring the quickstart located in Messenger Platform docs.
It’s an echo bot that responds to a user’s message by repeating their message back to them. It also sends a generic template when a message with “generic” text is received. This project is not dependent on any external libraries and can easily be extended.
To get started you need to:
Set up your Facebook app on Facebook
Configure your Facebook App
The Callback URL you set when configuring your app on Facebook is your Glitch project’s publish URL with ‘/webhook’ appended. The publish URL is what loads when you click ‘Show’ and has the format ‘https://project-name.glitch.me‘, so for this example we used ‘https://messenger-bot.glitch.me/webhook‘ for the Callback URL.
The Verify Token is a string you make up - it’s just used to make sure it is your Facebook app that your server is interacting with.
Copy your app credentials into the .env file
For more detailed setup instructions, see Messenger Platform Quick Start.