We were also having trouble and finally found a helpful post. I hope this might help you.
"Thank you.
I did contact support. and they were very helpful and got it figured out.
The issue was that the Web store had not had the shipping options set up. once that was done we were good to go.
Thank you and the team for all your help
Chris"
To resolve our issue, we went to our Dashboard > Fulfillment and setup shipping. I hope this helps you.
