plug&paid offers two options for sellers that wish to limit access to their checkout cart. These options can be enabled in the plug&paid settings page.
1) Automatically block your cart for visitors to whom you do not ship to: If this option is selected, then your visitors will be able to access your checkout cart(s) only if the products can be shipped to their IP location. This rule does not apply to products that do not have any shipping setup.
2) Checkout Country Whitelist: This option allows you to specify a list of countries from which users are allowed to access your checkout cart(s).
Note: If you activate both rules, then if you have checkout carts that contain both physical and digital products, then the Restrict Buyers rule is checked first.