PhpSpreadsheet 在本地主机上工作正常但不能在服务器上下载 excel 文件，出现一些错误

Question

我正在使用这个代码

include 'vendor/autoload.php';
use PhpOffice\PhpSpreadsheet\Spreadsheet;
     
if(isset($_POST["export"]))
{
  $file = new Spreadsheet();

  $active_sheet = $file->getActiveSheet();

  $active_sheet->setCellValue('A1', 'Zone');
  $active_sheet->setCellValue('B1', 'Customer');
  $active_sheet->setCellValue('C1', 'Competitor');

  $count = 2;

  foreach($all as $row)
  {
    $active_sheet->setCellValue('A' . $count, $row["depot"]);
    $active_sheet->setCellValue('B' . $count, $row["customer"]);
    $active_sheet->setCellValue('C' . $count, $row["name"]);

    $count = $count + 1;
  }
  ob_clean();

  $writer = \PhpOffice\PhpSpreadsheet\IOFactory::createWriter($file, $_POST["file_type"]);

  $file_name = 'Competitor Insights.' . strtolower($_POST["file_type"]);

  $writer->save($file_name);

  header('Content-Type: application/x-www-form-urlencoded');

  header('Content-Transfer-Encoding: Binary');

  header("Content-disposition: attachment; filename=\"".$file_name."\"");

  readfile($file_name);

  unlink($file_name);

  exit;
}

在服务器上出现此错误：

PHP 致命错误：未捕获错误：调用未定义函数 PhpOffice\PhpSpreadsheet\Shared\mb_strlen() 中 /home/spectra3/public_html/vendor/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Shared/StringHelper.php:451