Why do I get the error message, "Sorry, you don't have a prerequisite to purchase this pack," when trying to claim the Battle Bus (Titanium White) pack on the Epic Games store?

This happens when you do not have both the Epic Games Launcher and Rocket League installed on your PC.

1. Download Epic Games launcher: https://store.epicgames.com/en-US/download
2. Sign into your account.
3. Download and install Rocket League.
4. Launch Rocket League to ensure you are logged in on the same account.
5. Close Rocket League
6. In Epic Games Launcher claim the Rocket League- Battle Bus (Titanium White)
7. Launch Rocket League again to see the pack.