$_FILES empty after submit

$_FILES empty after form submit

I’m doing a little project where the user can upload multiple images from a simple form.
When I submit the form I go in a service page where I must save the images, but this not working.
So, I tried to print $_FILES, and I saw that it’s empty. Where is the mistake?

This is the HTML code with Boostrap:

<form action="salvataggio-foto.php" method="post" enctype="multipart/form-data">
  <div class="mb-3">
     <input class="form-control" type="file" id="images" name="images[]" multiple>
  </div>
  <button type="submit" class="btn btn-primary" name="invia">Carica</button>
</form>

In the service page, I have a simple print_r($_FILES).

Someone can helps me? Thank you so mutch 🙂