If it helps, I have a negative reputation at the moment as well and couldn't figure out why. My understanding is:
- "downvotes", which are called "reduces" on kbin, contribute negatively to your reputation score.
- "upvotes", which called "favorites", do not contribute to your reputation score in either direction.
- "boosts", which are similar to Twitter's retweet feature, are what contribute positively to your reputation score. When your comment/post/thread is "boosted" by another user, it shows up in the microblog/mastodon feeds of people following that user.
Maybe someone else more familiar with kbin and the fediverse can correct anything I have wrong.