Trying to check how many miles it would take for LON-AMS-BUD-LON.

It either tells me there aren't any flights in the timetable, or it hangs up for minutes.

On the phone, delta.com support says I should be able to book award travel on KLM through the Delta site - but the site sure doesn't seem to agree.

Note that this is not a codeshare I'm trying to book - there is no Delta codeshare from LON-BUD.

But how do I do it if KLM does offer that flight?