In-App-Purchase through an Application Store (Google Play, App Store)
If you receive an error code or a message from your platform when attempting to make an in-app-purchase, please contact customer support of the application store you installed the game client through.

Other
Your question hasn't been answered, or you need more information? Welcome to contact us through the Billing issue not listed section, and we will be happy to assist! Please describe your issue and attach some screenshots showing it for us to better understand its nature.