Disable WP JSON API

// Disable WP JSON API
add_filter( 'rest_authentication_errors', function( $result ) {
    if ( ! empty( $result ) ) {
        return $result;
    }
    if ( ! is_user_logged_in() ) {
        return new WP_Error( 'rest_not_logged_in', 'You are not authenticated.', array( 'status' => 401 ) );
    }
    return $result;
});