When I launch Capture Pilot, I am instructed to purchase the Camera Control App. Once I attempt to, I get the following message "You can't purchase this. You must first purchase the app that this item is for before you can purchase the item."
The issue may occur when you have more than one Apple ID. When the Capture Pilot is downloaded using an account that is different from the one with the help of which you are trying to purchase the Camera Control App.
To solve this issue, ensure that you have deleted the app on your iPad / iPhone.
Learn how to Delete App from iPad / iPhone.
Once the App is deleted from the device, delete it from iTunes as well to avoid any conflicts in the future.
Learn how to Delete App from iTunes.
NOTE: Make sure you are not connected to iTunes over a cable until completely done with the steps above.
Afterwards, go to Settings of your iPad/iPhone. Then go to Store and make sure to log in with the correct Apple ID. If needed, log out and log in to your account one more time.
Go to Apple Store on your iPad/iPhone. Search for the Capture Pilot application, download, and install it. Once installed, you should be able to purchase the Camera Control App.