Hi, @sibefitness
Greetings, and thanks for posting.
The error you are experiencing is actually within your current shipping settings. Generally when this error occurs it is due to a missing shipping zone, or a gap in your shipping rate conditions.
To test this, make sure you have added rates for all the zones (countries) you intend to ship to. Once that is complete, start reviewing your shipping rate conditions.
When I mention potential gaps in your rates, I am referring to either weight gaps, or price gaps. FOr example, if you offer a shipping rate for orders between $0-10, and the next rate is for orders between $11-20, you actually have a gap between $10-11. This causes any order that falls in this range, such as $10.50 to experience this error. To correct this, make sure your rates almost overlap, for example, $0-10 and $10-20.
I hope that helps! In the meantime, I’d love if you could provide a link to your store so I can take a look and provided additional feedback.