purchase.thank-you.block.render not rendering in app

[Kamaboko]

Just using the basic Shopify example to try and spin up a UI Extension app on the Thank you order page. Following this documentation: https://shopify.dev/docs/api/checkout-ui-extensions/2025-04/targets/block/purchase-thank-you-block-r...

import {
  BlockStack,
  reactExtension,
  Text,
  useApi,
} from '@shopify/ui-extensions-react/checkout';

// 1. Choose an extension target
export default reactExtension(
  'purchase.thank-you.block.render',
  () => <Extension />,
);

function Extension() {
  // 2. Use the extension API to gather context from the checkout and shop
  const {cost, shop} = useApi();

  // 3. Render a UI
  return (
    <BlockStack>
      <Text>Shop name: {shop.name}</Text>
      <Text>cost: {cost.totalAmount}</Text>
    </BlockStack>
  );
}

my extension.toml

[[extensions.targeting]]
module = "./src/Checkout.jsx"
target = "purchase.thank-you.block.render"

1. Confirmed app is installed, confirmed it works when using:

purchase.checkout.block.render

2. Confirmed added extension block in the scaffold via the theme > "Customize" 

anyone have any luck here?