Not sure what you mean by "multi-trip". If you provide a bit more information we can provide a clearer answer, but your post is so vague. Where are you travelling to, and from where?

Generally purely STAR travel cannot be booked on the website and require calling an agent. Also, travel in certain zones does not permit stopovers, so when you use the term you do, it might also be a factor of stopovers that are not permitted in these zones. Call AE.