<form action="{{ action }}" method="post">
  <input type="hidden" name="amount" value="{{ amount }}" />

  <input type="hidden" name="currency" value="{{ currency }}" />
  <input type="hidden" name="callback" value="{{ callback }}" />
  <div class="buttons">
    <div class="pull-right">
      <input type="submit" value="{{ button_confirm }}" class="btn btn-primary" />
    </div>
  </div>
</form>