It should report errors automatically. For the most part, it will detect problems automatically because a step will fail to execute. The reason is reported in the log that KIF creates. For example, if you had steps to (1) enter the user name (2) enter the password (3) click "sign in" (4) hit the refresh button

If the login failed for some reason, then step (4) would fail because it wouldn't be able to find the refresh button.

You can also add explicit verification steps, such as "wait for the view with the accessibility label 'Refresh'" if you want further validation.

Thanks!