New World Published But Invites Dont Work

Hi Everyone,

New to World creation, and just about finished the first world, I'm naming The Zone.  So I have published it as Visible, and open to all over 18.  If you search for "The Zone" your able to find it and go in, but when I try and invite friends they keep telling me Invite doesnt work.  So basically they got in only by means of searching it.  So they also tried to invite friends, and same issue, people say invites do not work?

Not sure what I am doing wrong, hoping someone here can help me?

Thanks