Why doesn't my submit button work?

The form is available when the user clicks a modal. When I click the submit button in the modal, it button does not work.

foreach ($posts as $post) { echo '
    <td>
      <button type="button" class="btn btn-success" data-toggle="modal" data-target="#$id_user">Validasi</button>
    </td>
  </tr>
</tbody>
';
}

Here is the modal:

echo '
<div id="$id_user" class="modal fade" tabindex="-1" role="dialog" aria-hidden="true">
  <div class="modal-dialog modal-sm">
    <div class="modal-content" id="registerContent">
      <div class="modal-header">
        <button type="button" class="close" data-dismiss="modal" aria-hidden="true">×</button>
        <div class="modal-text-header text-center">Validasi</div>
      </div>
      <div class="modal-body">
        <div class="container-fluid">'; echo '
          <form class="form col-md-12 center-block" action="http://localhost/MMM/admin/validasi/'.$id_user.'" method="POST" enctype=\ "multipart/form-data\">
            <div class="form-group">
              <input class="form-control input" placeholder="Dana awal (RP.1.000.000,-)" type="text" name="dana">
            </div>
            <div class="form-group">
              <input type="submit" class="btn btn-primary btn btn-block" name="submit" value="Submit">
            </div>
          </form>
        </div>
      </div>
      <div class="modal-footer">
        <div class="col-md-12">
          <button class="btn" data-dismiss="modal" aria-hidden="true">Cancel</button>
        </div>
      </div>
    </div>
  </div>
</div>' ;