For using Facebook Login in Spotter you need to create the Facebook App.
Go to https://developers.facebook.com/

Login with Facebook > Add a New App.

Go through all the stages of setting.

You can get APP ID and APP Secret code from Dashboard.

Go to Appearance> Spotter Options > Social connect > Facebook and fill App ID and Facebook secret code:

Finally you need to edit Sing in page > Visual Composer > Sing in form Setting > Show facebook connect button > Yes