Hello, it looks like the parameter is actually returnURL (and it’s case insensitive). I tested this on ee.kobotoolbox.org and found that both returnUrl and returnURL work properly.
I’m guessing in your case that it looked like it was sort of working because your Enketo server is also localhost:8080?
I haven’t checked—and this was not your question—but if you run into trouble with redirecting to complex URLs (e.g. that contain ? or & characters), try percent encoding them.
