When I connected my site and facebook I spent several hours in debugging issue with invalid parameter name in query(buggy example at https://developers.facebook.com/docs/authentication/server-side/
Right parameter name is `redirect_uri`, not `redirect_url`.
Eror message was `An error occurred. Please try again later.` and it doesn't explain the reason why this error happened. I suppose, in this case(and maybe some other cases with enabled sandbox or invalid app domain) error page should contain error message like 'Request dosn't have required arg redirect_uri'.