The one person I know getting paid to review AI outputs gets paid anywhere from $25 / hour to $40 / hour. Not sure if that's underpaid. It may be a nice option when you can do it at any time to supplement your regular income.
This person works through an interface which is similar to Mechanical Turk. You get a list of available projects you qualified for via an assessment. For the AI projects, many of them are comparing responses from two different models, answering questions, and selecting the best response. Other projects might be attempting to get the model to do something against the guidelines, or rating the model on certain capabilities. There's no requirements other than to pass the assessment. As with Mechanical Turk, you can work on your available projects at any time.