I agree. In the standard Racket IDE you get automatically the initial

  #lang racket

line, and in some variants for students the equivalent line is hidden. So I had to try a few times until I realized I forgot to add this line. https://tio.run/##K0pMzk4t@a@ck5iXrlAE4Sh5pObk5CuE5xelKP3/Dw...

Another improvement could be to show the debug output automatically. I didn't understand the problem until I read the error message.