@malte check to ensure your grid’s prefix is set to /grid as i described above. you can also edit the preferences text file that has the port information and manually set the prefix to /grid (you’ll need to do a grid hotplug after this)
more generally:
i’m sorry to say that i don’t have reaktor, and seemingly neither do many others here. does NI have a reaktor forum that might have some existing/working patches?
the best i can suggest is that we can explain how the OSC protocol works, but then you’ll need to take that information and translate it into reaktor.