Well for clarification just repeat the steps you need to follow for right purchase:

  • you have only one google account active on your device (Play has some issues in case you have two or more accounts synced)
  • validate your account is synced (mainly applications sync)
  • buy the product via Play (mention, which account is used for purchase)
  • receive license into email
  • update your product via button Premium (if the product will not do it for itself)
  • try to log with the same account you have used for purchase on your other android device
  • go to Play and install the product
  • you should see it as active purchase