Download Excel (phpExcel) by clicking the button

I am trying to download an Excel using the phpExcel library only when it receives a $ _POST parameter.

Currently I have a file called my-information.php where I have a table and a button that executes this function:

async function download_excel() {

     let myHeaders = new Headers();
     myHeaders.append("Cookie", "___asdadsadwqfqefqefqeeqasadsadsadasdsadas");

     var formdata = new FormData();

     formdata.append("generate_xlsx", 1);

     let requestOptions = {
          method: 'GET',
          headers: myHeaders,
          body: formdata,
          redirect: 'follow'
     };

     await fetch("<?= plugin_dir_url(__FILE__) ?>my-file-generator.php", requestOptions)
          .then(response => response.text())
          .then(result => console.log(result))
          .catch(err => console.log(err))
     }

In my my-file-generator.php file I have this code:

if (isset($_POST) && isset($_POST['generate_xlsx'])) {

    require_once '../../../../../wp-blog-header.php';
    require_once plugin_dir_path(__FILE__) . 'PHPExcel.php';
    require_once plugin_dir_path(__FILE__) . 'PHPExcel/Writer/Excel2007.php';

    $data = generate_data_for_xslx();

    // Create new PHPExcel object
    $objPHPExcel = new PHPExcel();

    $objPHPExcel->getProperties()->setTitle(esc_html__('Test xlsx document', 'woocommerce'));
    $objPHPExcel->getProperties()->setSubject(esc_html__('Test xlsx document', 'woocommerce'));
    $objPHPExcel->getProperties()->setDescription(esc_html__('Test export users document for XLSX, generated using PHP classes.', 'woocommerce'));
    $objPHPExcel->getActiveSheet()->SetCellValue('A1', esc_html__('User Login', 'woocommerce'));

    $cell_counter = 1;
    $objPHPExcel->setActiveSheetIndex(0);
    for ($i = 0; $i < count($data); $i++) {
        $cell_counter++;
        $objPHPExcel->getActiveSheet()->SetCellValue('A' . $cell_counter, $data[$i]['user_login']);

    }

    // Rename sheet
    $objPHPExcel->getActiveSheet()->setTitle(esc_html__('Users', 'woocommerce'));

    $objWriter = new PHPExcel_Writer_Excel2007($objPHPExcel);

    header('Content-Type: application/vnd.openxmlformats-officedocument.spreadsheetml.sheet');
    header('Content-Type: application/vnd.ms-excel');
    header('Content-Disposition: attachment;filename="usuarios.xlsx"');
    header('Cache-Control: max-age=0');

    // Save Excel file
    $objWriter = PHPExcel_IOFactory::createWriter($objPHPExcel, 'Excel2007');
    ob_end_clean();
    $objWriter->save('php://output');

    exit();
}

This way the file does not run, it does not download the Excel document. But if I copy the code that is inside the conditional and paste it in the my-information.php file, it executes perfectly when opening the page.

I tried adding the full conditional inside the my-information.php file and fetching the same file but it doesn't work either and the console gives me this error. Apparently the problem is to do it using the $ _POST parameter:

XHR POST https://example.com/wp-content/plugins/generateReporte/src/includes/my-file-generator.php [HTTP/1.1 404 Not Found 7578ms]

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    m��������X�(���)�����F���;@1�_������c)j�x/%����E��y�
�QĿi!��K��y3��J�<���Z�1��0?Y��L%zV
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I need to make the file generate and download only when I click the button, I have tried many ways and I can't do it, could you please help me.