una/modules/boonex/payment/template/redirect.html

__content__
<form name="bx-payment-redirect" action="__action__" method="__method__">
    <bx_repeat:items>
        <input type="hidden" name="__name__" value="__value__" />
    </bx_repeat:items>
</form>
<script language="javascript">
    document.forms['bx-payment-redirect'].submit();
</script>