Example to use this function

One need to add one custom field in lostpassword form using lostpassword_form hook, And now want to validate this field and add a wp_error also. So see how this can be done.

function wpdocs_mwb_cstm_pswd_post( $errors ) {
    if ( ! $department_valid_status /* The result of your department status*/ ) {
        $errors->add( 'invalid_department ', '<strong>ERROR:</strong> Try again later<strong>' );
    }
}

add_action( 'lostpassword_post', 'wpdocs_mwb_cstm_pswd_post' );