Facebook login “given URL not allowed by application configuration”

I've added facebook login to my site. However, when I click the button, I get a red box that says:

Invalid Argument

Given URL is not allowed by the Application configuration.

If I continue to login then I get:

API Error Code: 100
API Error Description: Invalid parameter
Error Message: next is not owned by the application.

Not sure exactly what the problem is. Any thoughts are appreciated.