Won't let me finish bonus chapter

I did all the games as far as I can tell, got the potion to give to the prince, but it won't let me move the potion to the prince from the bottom of the screen (playing on an android phone). The hint button circles the potion, then circles the prince, but even after exiting and re-entering the game, it still won't let me click on the potion and move it to the prince. Suggestions?

The same happened for me. Twice now. I completely closed the game/app and then I restarted my android phone (samsung galaxy 6s). It worked after that.