This is a simple python template that uses Flask to build a webhook for Facebook's Messenger Bot API.
Read more - repository is made using this tutorial.
New: Check out this Facebook Messenger Bot Course. It walks you through the process of getting this bot hosted on heroku step-by-step, and also unlocks all the content that's hidden in this repo's branches.
The #1 error that gets reported in issues is that facebook returns an error message (like above) when trying to add the heroku endpoint to your facebook chat application.
Flask application intentionally returns a 403 Forbidden error if the token that facebook sends doesn't match the token you set using the heroku configuration variables.
If you're getting this error, it likely means that you didn't set your heroku config values properly. Run heroku config from the command line within your application and verify that there's a key called VERIFY_TOKEN that has been set, and that it's set to the same value as what you've typed into the window on facebook.