Visit the Admininistration Tool -> Modules -> Payment page and install or confirm the module configuration parameters. (You shouldn't need to uninstall the previous module version)
Perform an order.
The line items are only added if the item totals equals the order total. It automatically adds extra order total values (eg discounts) as a line item however if the calculations do not equal the order total then only the order total is sent to PayPal. This is to make sure a transaction happens regardless. The PayPal Transaction ID is stored with each order and can be referenced with the transaction at PayPal.