I struggled with cables at first. You should be able to have a fiber connected to your camera and see the light come out the other end, this way you can take the strobe out of the equation and just focus on the fiber cable. I ended up needing to cut mine with a very sharp blade, too many reflections from the first time I made them when using a dull blade and the light wasn't getting through. As @makar0n suggested, I'm a fan (because of this site) of making your own if you're not in a rush. Ther are super easy to make, cheap, work well, and you can make any custom length and also have spares without breaking the bank and they will give you a good understanding of how they work and what to do if they aren't working.