This error appears at checkout when the cart contains a product that cannot be shipped to the selected delivery address.
When using a gift campaign, the gift product or its component products may be the cause.
Component product shipping settings issueCheck in the Shopify admin that the component products of the gift product are configured to ship to the relevant destination.
Insufficient inventoryCheck the inventory status of the component products and either restock them or enable "Continue selling when out of stock."
You can also check the inventory status from the campaign edit screen in the app. A warning reading "The gift product contains unavailable variants" may be displayed.
If the issue is still not resolved after trying the above, please contact our support team with the date and time the issue occurred, the campaign name, and the steps you took.