Cross Platform Cloud Save allows you to link your account to another platform (e.g. iOS, Android) and sync your save (progress, account rank, etc.) across. You only need this if you want to sync with a different platform . CivIdle has Steam Cloud enabled and will sync your save across different devices that runs Steam without this DLC. However, if you want to sync your save to another platform (e.g. iOS, Android), which Steam Cloud does not support, you will need to purchase this DLC. This DLC enables Cross Platform Cloud Save and does not add any content to the game. The price of this DLC is used to cover the server cost of hosting and syncing your save across platforms. How to Sync Save Across Platforms Purchase this DLC and restart your game Go to Options -> Manage Save and click Sync To A New Device to generate a passcode On a new device (iOS/Android), go to Options -> Manage Save and click Connect To A Device . Type in your player handle and the passcode You can now check in your save on one platform and check it out on another. To avoid save conflict, you can only check out your save on one platform at a time