Understanding this error from Shopify: "Your order cannot be shipped to the selected address."
Shopify will display the "Your order cannot be shipped to the selected address" error when it is unable to obtain shipping rate estimates during the checkout process. It can be a very misleading error because it seldom has anything to do with the address provided during the checkout process.
More often, the error occurs because there is an issue with the configuration of the shipping methods.
If you're confident that a valid address is being used, review the app's settings.
Also, consider modifying the message that Shopify displays in these cases. Contact Shopify customer support for assistance with this.
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Why Aren't My Shipping Rates Showing Up On My Shopify Store