Click the 'Product' button.
From the product list page click on the 'Set Up' button on the 'Messenger' product. The Messenger Platform will be added to your app, and the messenger settings console will be displayed.
Set Up Messenger Platform In the ‘Webhooks‘ section of the Messenger settings console, click the ‘Add Subscription’. This will subscribe your app to receive webhook events for the Page.
Webhooks on Messenger Settings On the pop-up subscription, choose ‘messages’, ‘message_deliveries’ and ‘messaging_postbacks’ to get started. Click the 'Save‘ button
Add subscription messenger is successful.
On the permission and features page, click ‘Request Advanced Access’ on page_messaging.
After that, all you have to do is wait for Facebook's response to your request.
