Haven't tried this recipe, Lisel, but I think you are right about the volume of water. I would put more in (perhaps 500 ml as the 50g may be a typo, i.e. they put in 50 instead of 500), keep an eye on it, and certainly add more water if it looks like it needs it. I would also chop the veges first. The varoma, reverse speed, etc. should be right for chopped veges, but do a taste or texture taste to check that they are cooked through after the 8 minutes, I suspect it may need more time.
If it is too thin or runny at the end, zap it briefly as chopping up the beans should thicken it up for you. Let us know how you go.