I have booked one way LAX to EZE using Avios on LAN (BA partner). I booked on line -- LAX to Lima, LIMA to EZE. I do not have enough Avios for the return, so I am try to see how much cash plus Avios I need for the return tickets. It is too early to book the return date.

When I try to put in a dummy booking for an earlier date (one that is bookable now), the website says "Sorry, BA and its partners do not fly this route." I get the same message when I put in the information one leg at a time.

Can anyone explain why this is happening?