I upgraded to iOS 7, why my plugins have disappeared?
You're probably running MovieSlate 4.0, which is not compatible with iOS 7. We released MovieSlate 7.0 with full iOS-7 compatibility on October 18. You'll need to upgrade as soon as possible, we consider this a critical update that resolves some serious issues introduced with iOS 7.
I've you've already upgraded to MovieSlate 7 and your plugins are not appearing then open MovieSlate, tap Settings, then tap MovieSlate Store. Tap the blue "Restore" button, enter the password for the iTunes / Apple ID you used to purchase MovieSlate and the app will contact Apple to get permission to install the plugins you previously purchased.