Originally Posted by
drwook
I don't know the 'official' answer but my experience has been hit and miss upgrading corp TA bookings. It doesn't just seem to be reward availability either. Could be it "should" always work but BA's site just doesn't play nicely, expect others can confirm that!
Tbh the website MMB function to do UuA is flaky so often it won’t work. Probably better just to call BA to do it.