Do I need the 'Carrier Calculated Shipping' add-on?
Addition can be used with all Shopify plans, including Shopify Basic. Furthermore, you do not need to purchase a 'Carrier Shipping' add-on. We have worked with Shopify to remove this restriction.
The only requirement is that your store is not running in development mode. That is, you must have selected a chargeable Shopify plan for your store.