Let's setup the in checkout validation together:

Step 1: Activate "In checkout validation" within AddressHero

Step 2: Open Shopify's "Checkout" settings

Step 3: Click "Customize" (please also make sure it is live)

Step 4: Add app block "addresshero-ext" within the delivery section

Step 5: Make sure "Allow app to block checkout" is activated

That's it. Now AddressHero in checkout validation is ready.