Hi mustweave,
Thanks for your message.
Cubasis offers the option to restore previous purchases via tapping the similar named button in the Cubasis In-App Store.
Making use of this option, please make sure you are logged in with the correct App Store account, used for your purchases.
If the problem persist, it might help to log off from the App Store, and give the iPad a full restart.
Please let me know if it helps to solve the problem.
Best,
Lars