Not sure if it's the same on your camera, but on some of the newer panasonic cams, you need to turn on [Focus Macro] in the settings. That way it can focus on an attached fisheye lens
Thanks for the tip! I had a look, but this camera does not have the Focus Macro -feature.
I seems that the issue is that this camera has a minimum focus distance of about 10cm, so it cannot focus to objects closer than that. I tried adding all the spacer rings I could find, 12 rings, and then I could focus the image
Maybe a macro filter between the camera and the fisheye could work?