I got into an extremely confusing situation where I worked across state lines. You have to report the income in both states, and both want to take the entire amount, unless those states have a reciprocity agreement.

I ended up filing incorrectly, claiming several hundred extra dollars in returns that I (probably?) didn't actually earn. This really looks like someone fraudulently claiming a credit for extra money.

The IRS sent me an email and a letter basically saying "hey you filed this wrong, but we fixed it, your actual return amount is this much less". End of story. I got my returns as expected and nothing else happened.

Honestly the simplest experience I have ever had with any agency of any government.