What is Carrier Shipping?
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 term 'Carrier Shipping' is often confused with traditional shipping carriers such as Australia Post, TNT, Fastway, etc.
Usually you would need a Shopify plan that supports Carrier Shipping to receive external rates, however we have worked with Shopify to remove this restriction on the Addition app.
You don't need Carrier Shipping to use Addition.
Addition does not require Carrier Shipping and can be used on all plan types.
It does not require you to have an Advanced or Plus plan, which support Carrier Calculated Shipping by default.
The only requirement on a specific plan is that your store is not running in development mode.
You can read further information on the topic of Carrier Service over in the Shopify help site.