Autoload and declare IOFactory before calling it

**require 'vendor/autoload.php';

use PhpOffice\PhpSpreadsheet{SpreadSheet, IOFactory};

use PhpOffice\PhpSpreadsheet\Writer\Xlsx; //Csv, Xls**

Before

$reader = IOFactory::createReader($inputFileType);

This solves your issues. Most of the tutorials on their site are not elaborate. Thanks