To sell the package of classes (a course), please see the video below:
to sell a course that has been planned in free mode you will have to click on "Course from Planning".
The difference between the first and the second type of sale is that the latter allows the choice of different days of the week
(e.g. if I sell a bi-weekly course I can pick a course on Mondays&Thursdays or Tuesdays&Fridays...), whilst the former has no multiple options.