This is the form,you may use for integration of PAY U,payment gatway,
<form method="post" action="https://secure.payu.com/api/v2_1/orders">
<input type="hidden" name="continueUrl" value="http://shop.url/continue" >
<input type="hidden" name="currencyCode" value="PLN" >
<input type="hidden" name="customerIp" value="123.123.123.123" >
<input type="hidden" name="description" value="Order description" >
<input type="hidden" name="merchantPosId" value="145227" >
<input type="hidden" name="notifyUrl" value="http://shop.url/notify" >
<input type="hidden" name="products[0].name" value="Product 1" >
<input type="hidden" name="products[0].quantity" value="1" >
<input type="hidden" name="products[0].unitPrice" value="1000" >
<input type="hidden" name="totalAmount" value="1000" >
<input type="hidden" name="OpenPayu-Signature" value="sender=145227;algorithm=MD5;signature=5fa8d94670eee6d182e930a0ccf9c2c6" >
<button type="submit" formtarget="_blank" >Pay with PayU</button>
</form >
you need to ensure,get all the values dynamically like the product name,price,quantity,etc. Also, check for more at
http://developers.payu.com/en/restapi.html