My Camera is connected to Vtuber Kit (technically), but it just won't record at all. My camera activates for like a second, but then it shuts off again. I never had this problem with my camera and it works fine anywhere else other than in VTuber Kit. I restarted a few times but that didn't fix it.

i have same issues.  Developer said there's no workaround and fix yet. I hope there will be soon

Check the older forum posts. It always seems to clear itself up within a couple days. I'm not sure why. It could be your antivirus blocking something, could be a random USB issue with needing to unplug and replug in the webcam. I don't think we ever figured it out. But anyone who had the issue had it resolved on its own after a while. Sorry I can't help more.