Checkout page when we get this warning
Solution
The Default Shipping Method can be set at Commerce > Websites > Website List > Edit Website > Shopping tab. If shipping items are not showing on the dropdown field on the Set Up Web Site page, these shipping items are not set to be displayed on the web store
To enable shipping item on the webstore
Navigate to Lists > Accounting > Shipping Items
Click Edit any shipping item
Ensure that the Display in Web Site is checked
If the Display in Web Site box is not present on the record, the Charge for Shipping option may not enabled. To enable it
Navigate to Setup > Accounting > Shipping
Charge for Shipping : Select Enable
Click Submit
Go back to the Shipping Item and the Display in Web Site and other options such as Shipping rate, etc. will be displayed