You can make a payment to the Artix Mobile game of your choice by choosing which upgrade package you would like to purchase in the upgrade shop and then you will be directly to pay via your Google Play account for Android device or your Apple/iTunes account via your iOS/Apple device.
Here is more information about in-app purchases and how to contact Google Play or Apple:
- Google Play - Apps with in-app purchases
- Apple - iTunes Store: About In-App Purchases