The in-app purchase in Manga Rock for iOS is tied to iTunes account. Once you bought the premium version, you can sync to any iOS devices for FREE. To do so, please follow these steps:
1. Make sure that your in-app purchase restriction is OFF
Step 1: On iOS device, open Settings > General > Restrictions
Step 2: Tap to Enable Restrictions. Enter the Restrictions passcode.
Step 3: Turn off In-App Purchases.
2. Restore in-app purchase
Step 1: Go to Device Settings > iTunes and App Stores
Step 2: Log in with the Apple ID you used to purchase the premium version
Step 3: Open Manga Rock app in your new device
Step 4: Log in and your account will be auto resumed as premium
Note: If the app won't automatically activate: open Account > Upgrade to Premium > Restore
After that, enter the same Apple ID and password to restore the premium version.
If you still fail to Restore, please tap on Buy now. Then, enter the same Apple ID and password you used to upgrade the premium version.