unable to upgrade iPad version from v8 to v9

I own a registration code for Pianoteq Standard. I've just upgraded my Mac to v9. I've tried unsuccessfully to upgrade my IOS version to V9. I downloaded V9 from the App Store. It loads in Demo mode. I'm presented with a message that I can upgrade my IOS version for $29.00. I click "restore purchases". I'm presented with a screen requesting my account login information (email, password). I start filling this in but before I can finish, this screen disappears and I'm taken back to the main interface which is still in Demo mode. How do I upgrade my iPad version?