Why am I getting a "Fortnite was not started correctly and needs to be closed" error message?

This can happen if you have other programs running in the background that interfere with Fortnite or networking issues.

First, make sure you are playing on a wired connection: Can I play multiplayer games on a Wi-Fi Connection?

If the problem continues, try creating a clean boot for Fortnite: How do I create a clean boot for Fortnite?