Hey!
That script is just an example for how a custom event script could be used to spawn an object at a character's location. If you make a new confetti prefab that uses a rect transform instead of a transform it might work? That said, particles aren't really meant to be displayed on Unity UI so some additional work might have to be done in that regard, too. If you have further trouble, I could try to write a script for you that spawns a gameObject at the right location after the holidays.