.If you build the shopping cart yourself in ASP, ASP.NET, PHP or any other server side scripting language, you can then just fire the total off to PayPal.
Here's the URL you need to submit data to:
https://www.paypal.com/cgi-bin/webscr
The parameters you need to pass:
cmd - set to _xclick
business - your PayPal e-mail address
item_name - Name of the item. You can just put 'Acme Order' (or whatever the company is called)
page_style - If you have custom page styles set up in PayPal, this is where you tell it which one to use. Otherwise it'll just choose default.
currency_code - Three letter currency code, like GBP or USD
amount - Ammount you will charge, with no currency formatting (so 3.99 as oppsed to £3.99)
invoice - It's a good idea to give a unique reference number to each order. Put it here to pass it on to PayPal
return - The URL that PayPal will redirect the user to once the transaction is complete
cancel_return - The URL that paypal will redirect the user to if they cancel payment
I have these in my URL... not sure if it needs them or not:
no_shipping=1
no_note=1
There may be more but I don't know of them.
A sample URL might be:
https://www.paypal.com/cgi-bin/websc...om/cancel.aspx
Don't use the Return URL as any confirmation to yourself that the user has paid up. It should just redirect to a 'Thank you for your order' page or simular - this is because people can copy and paste it from the origional URL, skip payment, and go straigt there. If you need to know the user has paid, check your accout manually before you ship the orders or use Instant Payment Notification (IPN)