There seems to be some confusion about the difference between the AppStore version of the game vs. the Steam version. You should be aware that these are 2 separate platforms and are not swappable or interchangeable.
Downloadable content will NOT work between platforms.
This applies to the following titles:
Borderlands: The Pre-Sequel
Civilization: Beyond Earth
Fahrenheit: Indigo Prophecy Remastered
Layers of Fear
WHAT IS STEAM?
Please let us know if you have any other questions and we will get you answers.