Sorry to hear you can't buy the next chapter, jeremyj.
When you say "nothing happens", do you mean no response at all? Or did the screen blink a bit. Or the icon highlighted, blinked, or called up an error?
Knowing more about the behavior can help track down logic in our game code.
What Android device are you playing on?
Knowing the specs of your device may help us track down possible technical factors.
Also, have you tried again since you've posted?
Sometimes it could be bad internet connection or Google Play Store may have been down for maintenance.