What does this error message mean for Fortnite?

What does this error message mean for Fortnite?

Means the patch could not be installed.

But he should try again later.

What do I have to do?

Ignore this… If you start fortnite and there's an update then this error message comes you must then just click on hide and load the patch

You can have your installation checked in the launcher (in the old one it was somehow called "verify"). There he checks all installed files and matches them with the one from the server. Do that. If there are missing / damaged files, he adds or replaces them. There's an option in the game under the launcher settings.