Gift Reggie normally works with Shopify variants directly. But many customers with more advanced themes may use Shopify line item properties. These extra properties include order information that's tacked onto your order when it's made. Many advanced apps such as "Product Customizer" use these to 'fake' additional products in your store. However, this significantly increases the complexity of registry management. If you’re using line item properties in your store, you may want to purchase a plan that can track custom properties, as this will enable to you to specify line item properties and additional meta-information on the registry itself.