The first time the app wants to access the camera, it will ask for your permission and pop-up a request. If you agree that, then the app will have permission forever. If you tap Don't Allow, the app will never ask for this permission again, which avoids the problem of an app repeatedly asking permission to do something you don't want it to do. In this case, you will see a camera icon with a line through it.
To enable camera access again, do the following:
1. Open the Settings app, and scroll down to the list of apps until you see Stop Motion Studio and tap it.
2. Make sure Camera access is enabled for the app.