A common error message associated with this issue is: "One or more items in your cart cannot be shipped to your region." This typically stems from a conflict within the shipping rate settings in your Shopify Admin.
Solution Steps
Follow these steps to resolve this issue:
Log into your Shopify admin
Go to Settings > Shipping and Delivery
Click Manage Rates in the Shipping
Scroll down to the bottom of the page where you'll find a section titled Not shipping from. You should see Single - App listed here.
Click on Add Rates > Use Same Rates
Click Done and save changes.