To follow and unfollow a person via a RESTful API, I have
What should these return in the body?
If you respond on errors using a HTTP server status, the status code does not say anything. If you respond with a 404 Not Found if there is no user Bob, or a 500 Internal Server Error if the database is broken, the only successful response you will ever get is OK. Users do not have to check the status code, they only have to check the HTTP status code.
I suggest you return nothing, and the fact that it is a successful response (i.e. 200 OK or 204 No Content) indicates that the operation was successful.