Hello,

The Checkout Field Editor (Checkout Manager) for WooCommerce and Vanilla are the third party plugins. As you want to remove the “billing_country”, “billing_state” and “billing_postcode” fields from checkout. The default WooCommerce does not provide such an option. As soon as the checkout has been filled out and there are empty fields, WooCommerce shows the notice.

Those fields are created as required by default WooCommerce functionality and also the functionality for validation is default WooCommerce, you can check with any default theme like twenty nineteen.

If you set “I sell to only one country” in WooCommerce settings, that country will appear in checkout and the country field will be read only and then hide the state field by using below CSS code in global custom CSS area under theme settings >> custom CSS:

You can hide it with some custom css:

#billing_state_field {
  display: none;
}

To hide the postcode field you can use the below code in funtions.php

function custom_override_checkout_fields( $fields )    
{
unset($fields['billing']['billing_postcode']);
return $fields;
}
add_filter('woocommerce_checkout_fields','custom_override_checkout_fields');

Best Regards.