So I need to ask a few things first:
1) Have you set up your cube with the particle app successfully (wifi settings, etc)?
2) If so, is your cube normally in "connected mode" when powered on or reset?
3) If so, does the "Send to Cube" button say "Flashing" (and begin flashing purple) some time after you clicked it?
If you answered "yes" to all above questions, then it means your cube is being flashed. Worth pointing out that "Spark Pixels v4" is a rather large piece of code and thus, it takes a considerable extra amount of time to complete flashing compared to other viz in the gallery. This is normal. You should wait until the photon LED goes back to "connected" (breathing cyan) and the cube will reset itself with the new viz that was flashed.
If you interrupt this process before it finishes, then the new viz will not be flashed and the cube is going to keep playing back the last successfully loaded viz.