Cześć wszystkim. Mam poniższy kod, ale kiedy klikam wygenerowany link, otwiera się nowa strona z wartością 0. Co robię źle?

function list_reservation_to_csv() {

 global $wpdb;
 $table_name = $wpdb->prefix . 'prenotazione_eventi';
 $file="email_csv"; // ?? not defined in original code
 $results = $wpdb->get_results("SELECT * FROM $table_name",ARRAY_A);

 if (empty($results)) {
   return;
 }

 $csv_output=""".implode('";"',array_keys($results[0])).'";'."\n";;

 foreach ($results as $row) {
  $csv_output .= '"'.implode('";"',$row).'";'."\n";
 }
 $csv_output .= "\n";

 $filename = $file."_".date("Y-m-d_H-i",time());
 header("Content-type: application/vnd.ms-excel");
 header("Content-disposition: csv" . date("Y-m-d") . ".csv");
 header( "Content-disposition: filename=".$filename.".csv");
 print $csv_output;
 exit;

 }
add_action('wp_ajax_csv_pull','list_reservation_to_csv');

$ajax_url = admin_url('admin-ajax.php?action=csv_pull');

<a href=" echo $ajax_url; ?>"><button>Scarica csv</button></a>