If you go to https://developers.facebook.com and edit your app, you then need to go to the left sidebar and under “Products” you will find “Facebook Login”. Expand it and click on “Settings”. Then in the “Valid OAuth Redirect URIs” field enter the following: http[s]://[yourwebsitedomain]/wp-content/plugins/wordpress-social-login/hybridauth/?hauth_done=Facebook and save the setting.
Be sure to replace http[s] with either http or https, depending on your setup and the [yourwebsitedomain] with your actual domain.
Then, in the “Redirect URI to Check” field at the very bottom of the page, put that same URL above in this message thread in that field and test it. It should come back as working.
Then, go to your website and test it.
This should work up until August 1, 2018 as at that point you need to submit an app review or it won’t work until Facebook reviews and approves it.
I hope this helps.