I found it but I still have 1 last question (I got the following code from a dead link through archive org where links today were dead).

What you see below is ActionScript2, tested and working.. My question is, am I able to add a "stock number"? (how many of that product that is available). What might the var string be?

Code:
var cmd:String = "_xclick";

var business:String = "paypal email here";

var item_name:String = "product name";

var item_number:String = "make your own product number or leave blank";

var amount:String = "price";

var shipping:String = "shipping price";

var no_note:String = "1";

var currency_code:String = "USD";

var lc:String = "US";

var bn:String = "PP-BuyNowBF";



buynow_btn.onRelease = function() {

	getURL("https://www.paypal.com/cgi-bin/webscr", "_blank", "POST");

};