fortnite - can my son play with someone who has fortnite on PS4?

You can do it

In order to play Fortnite across multiple systems, your son and his friend have to

link their Gamertag and PSN account to an Epic Account on the Epic website.

After that is done, they will have to add themselves as friends on the Epic website.

Then, when in the Fortnite game, your son needs to press the Menu button and navigate to Epic Friends.

If your son is under the age of 18, you might have to sign in with your parent account at
https://account.xbox.com/settings, choose your son's account, and set up his online and privacy settings to allow him to play cross platform.

This page here also has information on
how to crossplay Fortnite across different platforms.

Thank you I'll have a go....

yes you can, cross platform on fortnite has been active for a long time now, you need to add the ps4 player onto your epic games friends list, off the top of my head i cant remember how to do this but ones they are on each others epic friends list then they
can invite each other and play together on fortnite.

There are plenty of videos on youtube showing you how

https://www.bing.com/videos/search?q=youtube+add+ps4+players+on+fortnite+xbox&view=detail&mid=7C4C0C2043715C4FA9D57C4C0C2043715C4FA9D5&FORM=VIRE

There you go.

Thank you I hope this will work!

Yes he can cross platforming is available for this game between those two consoles I do believe a link needs to be created via epic.

yes you can, cross platform on fortnite has been active for a long time now, you need to add the ps4 player onto your epic games friends list, off the top of my head i cant remember how to do this but ones they are on each others epic friends list then they
can invite each other and play together on fortnite.

There are plenty of videos on youtube showing you how

https://www.bing.com/videos/search?q=youtube+add+ps4+players+on+fortnite+xbox&view=detail&mid=7C4C0C2043715C4FA9D57C4C0C2043715C4FA9D5&FORM=VIRE

There you go.