Can't load URL: The domain of this URL isn't included in app's domains?

Can't load URL: The domain of this URL isn't included in app's domains. To be able to load this URL, add all domain and subdomains of your app to the App Domains field in your app settings.

If you are facing an error of domain URL is not included in App's domain as shown below image, you just need to put put "Valid OAuth redirect URIs" and try to put a secure URL which uses https protocol using SSL because Facebook has updated his policy and require an https URL for this purpose.

 

Make sure options are chosen as displayed in below image.

 

And now put the OAuth redirect URL as shown in below image

 

Hope it solves your problem while making a Facebook App for social login or signup purpose.