I feel really stupid asking for help on this, but....
I recently won a stipula vedo off ebay (yay), except I am having problems getting the converter to fit properly. I see that there is a little plastic protrusion that sticks out from the back of the nib section:
but i can't figure out how to get the converter to fit snugly. I assume that the protrusion is supposed to fit into the open top of the converter, but for some reason it doesn't fit. I can't seem push it in directly either, nor does the push-and-twist mechanism seem to work:
So..what am I doing wrong?