How does billing when moonlighting work?

So this may have been discussed in a previous thread, but I wasn't really able to find anyone answering my specific question. From what I've seen on here in a few different sub-forums and threads, residents aren't able to bill for seeing patients until after they they've finished their residency. At the same time, from what I understand, people can start moonlighting as soon as they pass Step 3. So how does this work knowing that when they moonlight they sometimes are working on their own?... How does billing when moonlighting work?
Source: Student Doctor Network - Category: Universities & Medical Training Authors: Source Type: forums