getByUID returns api_parsing_error

Developing with Prismic
1

Getting error when calling .getByUID('homepage')

  response: {
    type: 'api_parsing_error',
    message: "[function at(..)] unexpected field 'my.homepage.uid' on line:1 col:6 in query '[[at(my.homepage.uid, undefined)]]'\n" +
      '[[at(my.homepage.uid, undefined)]]\n' +
      '     ^\n',
    pos: { line: 1, column: 6, id: 1, location: 'query' }
  },
  page: '/'
}
2

My bad, I forgot the contentType param.

.getByUID('page', 'homepage') works.