Facebook Webhook Subscriptions
Webhooks allow you to receive real-time notifications of changes to your Facebook page. For example, you can get notification whenever users post to your feed, comment on a post, or like your posts.
There are two steps for setting up Webhooks.
Step 1: Subscribe Facebook Page to App
Navigate to "Subscribed Apps" tab. Click on "Subscribe Page" button.
feed: Notifies you when an Page's feed has changed; posts, reactions, shares, and so on.
messages: Notifies you when your page has received a message via Messenger. For this, pages_messaging permission is required.
leadgen: Notifies you when lead form is submitted. For this, leads_retrieval permission is required.
Step 2: Subscribe App
Under App Subscriptions, click on "Subscribe App" button.