formula in phpOffice

Question

I use Symfony 4.4 and phpspreadsheet 1.28.0, how to enter a formula like $excel->setCellValue("D6", "=NB.JOURS.OUVRES(B4;B5)");

WHen I use this formula the page don't load

Thanks for your help

<?php

namespace App\Services\Factory;

.....
use PhpOffice\PhpSpreadsheet\Exception;
use PhpOffice\PhpSpreadsheet\Spreadsheet;
use PhpOffice\PhpSpreadsheet\Style\Alignment;
use PhpOffice\PhpSpreadsheet\Style\Border;
use PhpOffice\PhpSpreadsheet\Style\Color;
use PhpOffice\PhpSpreadsheet\Style\Fill;
use PhpOffice\PhpSpreadsheet\Style\NumberFormat;
use PhpOffice\PhpSpreadsheet\Worksheet\Worksheet;
use PhpOffice\PhpSpreadsheet\Writer\Xls;

class ExcelPointageFactory
{
    .......

    /**
     * @return void
     * @throws Exception
     */
    private function fillHeaders(): void
    {
        $excel = $this->sheet;
        $excel->setCellValue("D6", "=NB.JOURS.OUVRES(B4;B5)");
    }