You’re getting a 400 status code in this case with this body:
{“errors”:[{“code”:21,“message”:“Contributors are not enabled for the specified user”}]}
Which indicates that the user you’ve requested doesn’t have contributor mode enabled on it.
Contributor mode is a seldom found feature that some Twitter accounts have. It lets other authorized users sign in to the account and tweet and perform other actions on that account’s behalf. With @twitterapi, a number of us on the platform team have the ability to tweet from that account, for example.