Fortnite is a hugely popular game and is not without issues from time to time. One problem that players run into is random log-in errors. Sometimes, when trying to get access to the game, players will get an error message that says you do not have permission to play Fortnite.
Unfortunately, there is little that players can do to solve this issue. The cause of it seems to be an error when it comes to reading your account profile privileges. As such, the authentication server cannot read whether you have “permission” to play Fortnite, so cannot correctly log you in.
By permissions, we normally mean legal ownership of a game, but as Fortnite is free-to-play it is more than likely checking to see if your account is in good standing and has never been banned for cheating or any other reason.
All you can do right now is be patient and wait for Epic Games to solve the issue. The good news is that they are aware of issues that are ongoing at the time this article was published and will be working hard to resolve them as quickly as possible. Be sure to follow the Fortnite Status Twitter account for updates on the game, as they will send a tweet when the issue is resolved.