i keep getting this error "Your order cannot be shipped to the selected address."

Hi, whenever a customer tries to purchase a product from a diffenrt country, they get the error:

“Your order cannot be shipped to the selected address. Review your address to ensure it’s correct and try again, or select a different address.”

how can i fix that please!

Thank you for your help, I’ve tried all these, nothing’s working and i dont know how to contact shopify support