Hey there! Digital Artisans here! For this it is worth going to check your shipping profiles and settings. To do this go to the settings section of the Shopify store and then select Shipping and Delivery. After selecting Shipping and delivery select manage shipping rates and go to your shipping profiles, here you will be able to see all the countries your store ships to and the rates.
You just need to check you have the country in your shipping settings that the client is trying to order from. If not you can add it by creating a shipping zone or editing the one you have active ! If you need anymore help let me know.