To purchase a registration, highlight the level on the list at the left side of the screen. Then click Add to Shopping List. Similarly, to remove an item from your list of things to be purchased, hilight the item on the right side of the screen and then click Remove from Shopping List. You can edit the quantity to purchase and the level by double-clicking an item in your shopping list.

If you wish to purchase more than one level of registration, you should do so in separate transactions to ensure that your purchases are properly recorded.  However, multiple purchases of the same registration level (e.g. purchasing two copies of Level 3A for inclusion with your own commercial products), can be done at the same time.