Paypal integration questions - asp.net

Question

I have some code that i wrote many years ago to integrate Paypal within my site. So a user adds multiple products to their cart and then checks out which then automatically takes the user to the paypal site.
I decided to revisit it today and created the following HTML
<form name="myForm" method="POST" action="https://www.sandbox.paypal.com/cgi-bin/webscr" >
<input type="hidden" name="cmd" value="_cart"/>
<input type="hidden" name="business" value="myemail-facilitator#myDomain.com"/>
<input type="hidden" name="item_name" value="Product 1"/>
<input type="hidden" name="amount" value="500.00"/>
<input type="hidden" name="quantity" value="1"/>
<input type="hidden" name="upload" value="1"/>
<input type="hidden" name="currency_code" value="GBP"/>
<input type="hidden" name="return" value="http://XX/paypal/completed.aspx"/>
<input type="hidden" name="rm" value="2"/>
<input type="hidden" name="cancel_return" value="http://XX/paypal/Cancel.aspx"/>
<input type="hidden" name="shopping_url" value="http://XX/paypal/MyShop"/>
<input type="hidden" name="notify_url" value="http://XX/paypal/MyShop/checkout.aspx"/>
<input type="hidden" name="lc" value="GB"/>
<input type="hidden" name="image_url" value="http://XX/paypal/shop.gif"/>
<input type="hidden" name="no_note" value="1"/>
<input type="hidden" name="invoice" value="ZZZ1234567890"/>
<script type="text/javascript">document.myForm.submit();</script></form>
This came up with an error "Error Detected Your shopping cart is empty".
Logged into my sandbox account and no error listed to determine what ive done wrong.
Googled around which suggested to change _cart to _xclick - which resolved the issue, however when i read the documentation at
https://developer.paypal.com/docs/classic/paypal-payments-standard/integration-guide/Appx_websitestandard_htmlvariables/
I dont understand why _cart didnt work? Is there a more appropriate way to do this or _xclick fine with my site setup as described above?
For multiple items i was looping the item_name and amount and adding each value, but this doesnt work the way i expected i.e. I've seen sites where they display each product, quantity and amount for each product in the cart and then total - where did i go wrong?
Finally once a transaction is complete i have set up the IPN value to send the details to my site..... Do i need the site to be using https in order for this to work or would http work?
I tried searching for these answers but some are quite dated or using 3rd part components.

Answer 1

Please make below changes to your HTML codes to make your form work again.
<input type="hidden" name="item_name" value="Product 1"/>
<input type="hidden" name="amount" value="500.00"/>
<input type="hidden" name="quantity" value="1"/>
↓↓
<input type="hidden" name="item_name_1" value="Product 1"/>
<input type="hidden" name="amount_1" value="500.00"/>
<input type="hidden" name="quantity_1" value="1"/>