Please regularly watch and follow the instructions in this video
The most important things when zipping/unzipping are...
1.  Always hold the handle and pull away from the handle
2. Always move the zip slowly and smoothly
3. Always hold the zip toggle with your 2 fingers
4.  Always use the blue tube and hold it with your fingers flat like a letter
5.  Always make sure the sip is wet/lubricated
6. Try to have the ball positioned horizontally with the zip flap at the bottom
7.  Never force the zip or do it fast/any other way than described above and explained on the video
8.  Always dry and clean the balls after use, never pack wet/damp/dirty into bags when not in use)