Unfortunately, due to recent changes in Shopify's policies, it's not possible to run tests or modify the checkout page using external tools like Mida.

Shopify has deprecated the ability to edit checkout.liquid, which means we can't load our script or apply CSS changes to the checkout page. This change affects all third-party A/B testing and personalization tools.

For the most up-to-date information on what's possible with Shopify checkout pages, we recommend checking their official documentation.