1. Navigate to your Shopify Shipping & Delivery Settings.
2. Click on your General shipping rates.
3. Scroll to the "Shipping origins" section.
4. Select "Show details".
5. Click "Manage" to the right of "Carro Partnerships"
6. Select "Create new rates".
7. Scroll to the new "Shipping origins: Carro Partnerships".
8. Click "Create zone".
9. Name the zone. Suggested: "Domestic Carro".
10. Search "United States".
11. Un-check Territories and other non-States. Click "Done".
12. Choose "Add rate".
13. Choose the Rate Name tied to your free shipping, and set the Price to $0.00. Click "Done".
Please keep in mind that the normal Shopify shipping rules apply in regard to naming shipping rates. More information from Shopify is available here.
14. Click "Save".
15. Complete. To test, add a Carro product to your cart to confirm no shipping is charged at checkout.