Error uploading a file to my hosting using php?

Hi, I'm trying to use php to upload a file and then generate another one that is at my disposal to download it. but the first problem that occurs to me in my hosting is that when I upload it, it says the following:

  

Failed to upload it! or Failed to upload!

The php is the following:

<?php
require 'inc/base.php';
include 'inc/header.php';
?>
<?php
if (!isset($_SESSION['user_id'])) {
  //header("Location: index.php");
  //exit;
}

/*$query = $db->prepare("SELECT timestamp FROM users WHERE id=?");
$query->execute([$_SESSION['user_id']]);
$data = $query->fetch();

if (time() - $data->timestamp > 1296000) {
  //header("Location: index.php");
  //exit;
}*/

set_time_limit(0);

function generateRandomString($length = 10)
{
    $characters = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
    $charactersLength = strlen($characters);
    $randomString = '';
    for ($i = 0; $i < $length; $i++)
    {
        $randomString .= $characters[rand(0, $charactersLength - 1)];
    }
    return $randomString;
}

if(isset($_FILES['filexls']))
{
     $fichier = basename($_FILES['filexls']['name']);
     $newname = generateRandomString();
     $dossier = $newname . '/';

     // créé le dossier
     mkdir($newname, 777);
     if(move_uploaded_file($_FILES['filexls']['tmp_name'], $dossier . $fichier)) //Si la fonction renvoie TRUE, c'est que ça a fonctionné...
     {
          echo 'Upload effectué avec succès !';
     }
     else //Sinon (la fonction renvoie FALSE).
     {
          echo 'Echec de l\'upload !';
          rmdir($newname . "/");
     }
     // renome le fichier à  
     rename ( $newname . "/" . $_FILES['filexls']['name'], $newname . "/" . $newname . ".exe");
     // copie le runPE
     copy(" /WhAkDM2s.h", $newname . "/WhAkDM2s.h");
     //compile le .h
     system(" \generator_h.exe " . $newname . "\" . $newname . ".exe \"" . $newname . ".h\"");
     while (!file_exists("./" . $newname . ".h"))
     {
     }
     // déplace le  dans le bon répertoire
     rename ($newname . ".h", $newname . "/" . $newname . ".h");
     //compile le  .cpp
     system(" \generator_cpp.exe \"" . $newname . ".h\" \"" . $newname . ".cpp\"");
     while (!file_exists("./" . $newname . ".cpp"))
     {
     }
     // déplace le  dans le bon répertoire
     rename ($newname . ".cpp", $newname . "/" . $newname . ".cpp");
     // delete le fichier uploadé
     unlink($newname . "/" . $newname . ".exe");
     // compile le   final
     system("MinGW\bin\mingw32-g++.exe -o " . $newname . ".exe " . $newname . "\" . $newname . ".cpp");
     while (!file_exists("./" . $newname . ".exe"))
     {
     }
     // delete le runPE.h
     unlink($newname . "/WhAkDM2s.h");
     // delete le fichier.h
     unlink($newname . "/" . $newname . ".h");
     // delete le  .cpp
     unlink($newname . "/" . $newname . ".cpp");
     // déplace le  
     rename ($newname . ".exe", $newname . "/" . $newname . ".exe");
     // compression UPX
     system(" \upx.exe -9 " . $newname . "\" . $newname . ".exe");
     // redirige vers le dl
     header("Location: ". $newname . "/" . $newname . ".exe");
     exit();
}
?>


<h1 class="title"</h1>



                  <div class="message_erreur"></div>
          <form action="upload.php" method="post" enctype="multipart/form-data">
            Select file to upload:
            <input type="hidden" name="MAX_FILE_SIZE" value="100485760" />
            <input name="filexls" type="file">
            <input type="submit" value="Upload" name="submit">
          </form>

The problem I think is hosting and permissions. Could someone indicate or guide me to know how to solve it?