If you are getting an error stating that you do not have shipping rates available for an address, then it would indicate that you do not have shipping rates set up for that specific country in Settings/Shipping.
Shipping rates can be per location, meaning that you may have shipping rates set up for one location but not the other. An example would be if you have your product inventory being held in location “A” but your shipping rates are set up for location “B” - Since you do not have inventory in location “B” the shipping rates you created will not be used. You would need to ensure you have shipping rates for all of your locations/app locations, or transfer your inventory to the proper location. You can learn more about transferring your product inventory here.
You can view your locations in Settings/Locations. Here you can disable any unneeded locations, or add a new location if required. You can learn more about locations here.
If you have your products in the correct location and have shipping rates set up for the region you’re trying to purchase from but are still seeing the error, then I would recommend contacting Shopify Support. You can do this by logging into your store through the help center, searching your question/issue, then selecting “continue” at the bottom of the page that displays the search results.