Our app has a few in-Checkout validation features that you can review here:
In-Checkout Validation overview
We cannot fully validate in-Checkout since Shopify doesn't technically allow apps to block the checkout at the address step on non-Plus plans.
⚠️ Why this limitation exists: Shopify only allows apps to block a checkout via Checkout Extensions on Shopify Plus. On standard plans, AddressHero validates post-checkout (on the Thank You page) instead – which catches the same errors without impacting conversion.
What AddressHero validates post-checkout
Missing house number
Incorrect or unrecognized street names
Wrong postal code / city mismatch
Packing station format errors
On Shopify Plus, you can also block the checkout directly for redirect-based payment methods – see this article.