Why is the pincode checker not showing on my product page?

The checker only appears when all of these are true. Check them in Plugins → Delivery Restrictions → Settings:

1. Enable pincode restriction is ticked. While it is off, every pincode is treated as serviceable and the checker stays hidden.
2. Show on product page is ticked. Cart and checkout have their own switches: Show on cart and Show on checkout.
3. You clicked Save settings after changing them.

The Delivery Restrictions plugin must also be active for your store. If it is not, the admin page shows "plugin is not active" with a Go to Plugins button.

Once it is working, shoppers see Check delivery availability with a pincode box and a Check button.