1. Both sectors were available individually, which is why the frustration with this booking error. If there was simply no award space that would be fine.

2. Used the Whatsapp - seemed to be quite helpful. The actual date I want to fly is in mid Feb (this was a test run) so I didn't go through with the booking, but the agent confirmed this ticket was valid, should be bookable and it was likely a website error. 108,400 miles which is a steal for a one way to LHR with the long leg in F! Will try for the date I actually want towards the end of next week.