"Pandas like sleeping."
I would say it is not required. But 很 is weird character in this course because sometimes it is used to emphasize what that you like something, and other times not. Duolingo don't seem to be very clear about this.
I think the answer should be "Panda's really like sleeping" or Pandas like sleeping very much".
In other parts of the course they use 喜欢 without the 很
Like 我喜欢喝咖 for example.