Shopify have recently updated the Order Confirmation and Thank You pages that the Address Check & Validation app works in.
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The changes mean that this app is no longer able to function with these updated pages and we have announced the end of sale and end of life of this app to all merchants using it.

The app will continue to work in any older stores which have not upgraded to the new Order Confirmation and Thank You pages but all new stores have these updated pages by default, meaning the app cannot be installed.

If you are using the app on a Shopify Plus Store we recommend switching to our Data Validation app specifically built for Shopify Plus.