https://www.gamespot.com/articles/ps4-and-xbox-one-cross-play-was-live-in-fortnite-b/1100-6453406/

From a technical standpoint, the ability for PS4 and Xbox One owners to play online together in games like Rocket League is more than possible, but to date, Sony has not given its consent to allow it to happen. Despite that, Fortnite reportedly enabled cross-platform play between the two consoles over the weekend, although that has now been turned off and chalked up to an error.