Hello--I think what you're looking for can be found in more detail here: https://developer.apple.com/documentation/appstoreservernotifications. Hope it helps!

AFAIK, you cannot do that through the App Store. You should be able to use deep link to navigate to App Store and then download the app. App Store redeem flow is only meant for Gift Cards as of now. The reason this is not allowed is because multiple developers can end up using the same custom code, which Apple has no control over. For example: for a new years campaign you can have two different developers using the same NEWYEAR2024 code.