Paypal IPN using PHP to get customized Quantity and Amount

I have downloaded the sample paypal IPN script using php and customised with the email for the buyout option and it has also some hidden paramaters such as amount, quantity,开发者_开发技巧return_url, notify_url like this. My main idea is to do the buyout option for the product purchase in my website.The current calculation for the product purchase is as follows:

      Item Price:$20
      Quantity  :10
                           Total amount $200

I need the calculation to some different way as our site have some static set of quantities and prices, so our point of calculation is as follows:

       Item Price:$20
       Quantity  :10    

                           Total amount:$20

So, the total amount needs to be the same for the given number of quantities.The IPN configuration doesn't allow me to change the quantity field by this way, please suggest some ideas to overcome this issue.

The item price is price per item, the quantity is of course multiplied by the item price. Your second example should have $2 as the --Item-- price. If you want to sell "10 items for $20", I think you will need to make a new item for that combo and just but the actual quantity in a custom field.

If you want to use the same item and paypal's quantity field, I think you need to look into calculating a discount and making that part of the parameters (discount_amount_cart or discount_amount_X for item X I think).