If you want to charge a fee for international shipping but not domestic shipping when using either the INTERNATIONAL SHIPPING add-on or the INTERNATIONAL FORCED PRODUCTS add-on, you can simply enter a series of zeroes in the product ID area of the configuration and when a chosen domestic country is selected, no product will be associated or added to the cart (hence making domestic shipping free)....
Just use this as you are domestic product id: 0000000
If you run into troubles, please don't hesitate to reach out to our support desk. Thank you!