Why can I not select Friends-only party privacy for the bot?
This panel supports Public and Private party privacy. Friends-only is not an accepted value, even if you have seen that option in another tool.
Use an offered choice
Open Attributes and chat, choose Public or Private under Lobby privacy, then select Change for the connected bot.
Read a rejection
If a console command using friends is rejected, choose a supported value instead of repeatedly resending the same request.
Check the party itself
Inspect the resulting party in Fortnite and keep your player leading the normal setup. A party-privacy change does not establish a private matchmaking server.