<?
// hash отправляемых данных с ключем
$sign = md5($ID_PURSE .'::'. $pay_id .'::'. $pay_cost .'::0::'. $pay_desc .'::'. $SECRET_KEY);
?>
<form action="http://bank.smscoin.com/language/russian/bank/" method="POST">
  <input name="s_purse" type="hidden" value="<?= $ID_PURSE?>" />
  <input name="s_order_id" type="hidden" value="<?= $pay_id?>" />
  <input name="s_amount" type="hidden" value="<?= $pay_cost?>" />
  <input name="s_clear_amount" type="hidden" value="0" />
  <input name="s_description" type="hidden" value="<?= $pay_desc?>" />
  <input name="s_sign" type="hidden" value="<?= $sign?>" />
  <button type="submit" class="btn btn-success"><?= __('Оплатить')?> <?= $pay_cost?> руб.</button>
</form>