After you completed the setup process, you can see the shopping cart and order form links of the product. The link looks as:
https://www.swpal.com/order.php?items=xxxx-xxxxx&clear_cart=true
"xxxx-xxxxx" is a compilation of vendor ID and product ID. To put multiple products in shopping cart with one link, you can create a link with comma to separate product IDs as:
https://www.swpal.com/order.php?items=vendorID-productID1,productID2...
Parameter "clear_cart=true" resets shopping cart and it is required for subscription products. You can also include parameters "additional1" and "additional2" to pass extra information into orders. If you would like to create the orders with a coupon ID by default, you should add a parameter as "couponID=xxxx" to the links.