I tried to look into making custom rewards for chance cubes and it turned out to be really easy looking, so I went off and did some work and made some custom rewards.
I then noticed the "Sounds" folder and wanted to test around to see if I can get a sound to play when the chance cube reward is triggered, in order to add to the "coolness" factor.

unfortunately I cannot figure out for the life of me how to get it to work.
I put the sound in the "Sounds" folder under "Custom Rewards" in the config
I made sure the sound is a .ogg format
and from my knowledge I referenced the sound in the custom reward properly by referencing it as "chancecubes.soundname"
(or the full line being "sound":"chancecubes.soundname")

I'd like to know If I'm just being dumb and not knowing what I'm doing or if the custom sound system is just currently not working in the most recent version

I am using Minecraft version 1.12.2
and mod version "ChanceCubes 1.12.2-3.1.0.217"

Seems I fixed it in 1.10.2, but it didn't carry over to 1.12. I will fix this when I can!