I found a very insightful article on team motivation and rewards at https://medium.com/@AgilePHL/intrinsic-motivation-the-virtual-kudos-box-3b0bcedbbd6f
Well worth the read, but here’s the summary:

However, there are several truths that will remain resolute:

  • Don’t promise rewards in advance.
  • Keep anticipated rewards small.
  • Reward continuously, not once.
  • Reward publicly, not privately.
  • Reward behavior, not outcome.
  • Reward peers, not subordinates.