The Full Version of iStudiez Pro for iOS allows you to sync on your iOS devices. 

So there's no need to buy the Full Version separately for iPhone and iPad.

If you have bought the Full Version for iOS e.g. on iPhone, but asked to pay on e.g. iPad, 

please do the following:

1. Create iStudiez Pro data backup on a device with the latest app's data

2. Uninstall the app from your iPad 

3. Sign in to the App Store under the Apple ID you have used to buy iStudiez Pro on your iPhone

4. Install the app on your iPad

5. Sign in to your iStudiez Pro Cloud Sync account.