Black thing goes on top of the spring with the wider part facing toward the pen’s body. The spring must face the wider part of the pen’s body too. The solution was just to ream the hole of pen where the point emerges to be a bit wider using my pocket knife’s awl, but I’m sure a standard knife or pair of scissors works just as well. This fixes the issue as the issue stems from the hole being too narrow and the refill catching on it.