<form id="payment" method="post" action ="intercards-api-url">
<input type="hidden" id="token" name="token" value="merchant-token-here"/>
<input type="hidden" id="order_id" name="order_id" value="order_id-token-here"/>
<input type="hidden" id="sum" name="sum" value="payment-sum"/>
<input type="hidden" id="email" name="email" value="customer-email"/>
</form>
<form id="payment" method="post" action ="intercards-api-url">
...
<button type="submit">Оплатить</button>
</form>
<script type="text/javascript">
var form = document.getElementById('payment');
form.submit();
</script>