Find Facebook Page ID

From the Facebook  Page

At ‘Page‘ Tab ->  ‘About‘ Tab,

Can notice Page ID.

Enter that Page ID in WP-Chatbot plugin Settings page

One Important step is to add Messenger on Website to Whitelisted Domain

( Add domain name at Facebook page Settings -> Messenger Platform -> Whitelisted Domain )

Or another way to find Facebook Page ID, if you are not an admin this will be useful. ( External link )