Sign in to your Epic Games account
Open Fortnite on Xbox
Go to the main menu
Select the Settings gear icon
Open the Account and Privacy tab
Make sure Cross-Platform Play is enabled
Set Cross-Platform Matchmaking to On if available
Save the settings
Add friends using their Epic Games display name
Invite cross-platform friends to your party
Check Xbox privacy settings if cross-play is blocked
Allow multiplayer and cross-network play in Xbox privacy settings
Restart Fortnite after changing settings