add_action('template_redirect', function() {
  if (is_page('208')) {
    $referer = array('https://digital-jinja.com/sanpai/', 'https://buy.stripe.com/test_aEU3eR1af5EA6Q07ss');
    $arrlength = count($referer);
	for($x = 0; $x < $arrlength; $x++){  
        if (!isset($_SERVER['HTTP_REFERER']) || $_SERVER['HTTP_REFERER'] !== $referer[$x]) {
            wp_safe_redirect($referer[0]);
            exit();
        }
    }
  }
});