What is Carrier Shipping and why is it required?
Carrier Shipping or Carrier Calculated Shipping is a module within your Shopify store which facilitates your store's ability to retrieve rates from an external shipping app.
This module is often confused with traditional carriers such as TNT, FedEx, Australia Post and many more. These are traditional shipping carriers but they are not what Shopify calls 'Carrier Shipping'.
Requirements for access to the Carrier Shipping service.
If your plan meets any one of the following criteria it will qualify for Carrier Shipping.
It is on the Advanced Shopify plan or Shopify Plus plan.
If your Shopify plan is billed annually.
It is a development store.
You can read further information on the topic of Carrier Service over in the Shopify knowlege base.