I have beaten the first level three times now. Each time it crashed my Playdate with an error message that reads: 

main.lua:1202: attempt to index a nil value (field '?')

stack traceback:

  main.lua:1202: in function 'HandleBall'

  main.lua:1308: in function 'MoveBalls'

  main.lua:729: in function <main.lua:701>

On a side note, it is currently possible to hit the balls at such an angle that they endlessly bounce back and forth against the walls in a straight line. I know it was a straight line, because it was just above the paddle and the game wouldn't end because the balls were still in play. 

Thanks for this game! Hopefully this helps. 

I got this exact same error after completing the first level, but I had multiple balls going in different directions

I have hopefully fixed  both issues