Api function 'Get presenter by id' delivers empty array only

In 'API Reference' I use the function 'Get a list of the presenters' and get a list of presenters. Then I take the first Presenter ID (e.g. 'amy-Aq6OmGZnMt') and call the function 'Get presenter by id' and get only an empty list.
What's the reason? How to get the desired data?