Login error

My brother is a codechef daily user & his account is attached with facebook account &login in codechef through facebook,till yesterday everything was fine but today he is not able to login his account & every time “Your facebook authentication failed” is showing .
pls.Someone can suggest how to fix the problem…

Try to login your facebook on device. Maybe someone may have changed the facebook’s password of that account.

Thank u yash for help,after trying sometimes, now problem is resolved.