The credits are needed to use One-Click Apps only, unless you have the VAG ULTIMATE plan in which case all One-Click Apps for VAG group vehicles are free and unlimited to use!

You can check:

What are One-Click Apps and how to use them on iOS?

What are One-Click Apps and how to use them on Android?

For a better price, you can purchase credits on the website HERE or from the application on the Google Play Store, App Store, or HUAWEI AppGallery.