This article explains why you can't transfer your previous in-app purchase in one platform (Android or iOS) to another platform (iOS or Android).
In-app purchase is NON-TRANSFERABLE between platforms.
We are very sorry to inform you that if you have bought the app on iOS, you can't restore your purchase on Android or vice versa.
In-app purchase procedures for both Android and iOS platforms are strictly defined by Google and Apple. They will not allow us to modify their procedures in any way. If we do so, Manga Rock might be removed from the Play Store / App Store.
In fact, we have tried to do this once before; as a result, our Manga Rock app was taken down from the Play Store by Google.
We sincerely hope to have your understanding and continued support for Manga Rock.