Create new chat room apps

Can someone help me about create new chat in acs appcelerator.

This is my code :

Cloud.Chats.create({

        to_ids: ids.join(','),

        message: message.value

    }, function(e){

        if (e.success) {

            for(var i = 0, l = e.chats.length; i < l; i++){

                receiveNewMessage(e.chats[i]);

            }

        } else {

            alert('Failed sending chat');

        };

    });

but, it's define error in "to_ids: ids.join(',')". what are I created into ids.join?

Thank you.