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.
https://findmyfbid.com/ ( External link )