Hi,
after playing part 1 and 2 (in-app purchase done without any problems) I am now not able to buy part 3 (days 4-6).
Whenever I click on the corresponding icon with the lock on it, I just get a dialog box saying:
"ERROR. Authentication is required. You need to sign into your Google account."
The only interaction possibility I have is an Ok-button, which closes the dialog box. There is no chance to enter my password.
The strange thing is, that for part 4, everything was normal. There, the dialog box with the price opened up where I could also enter my Google password. I did that hoping this would fix my problem with part 3, but it didn't. So I am now left with part 1, 2 and 4, but no 3 to continue with

I am using a Samsung Galaxy Tab S (SM-T800) with Android 5.0.2. I have tried restarting the program and the tablet many times. I also changed my Play Store setting from "authentication always required" to "authentication never required", but with no success. I just keep getting the above error message.
Searching for that error in Google shows that it seems to be no uncommon problem to developers when implementing in-app purchases. I hope you can help me. I really want to continue with the great game and I really wish, I had chosen the PC version without all this in-app purchase stuff.
Greetings,
Holger
PS: One more fact that might help you: When I got the game, I clicked in the icons of all parts in the menu to see, what they cost. If I remember correcty, the dialog box with the price opened up correctly for part 3. But I closed it and opened part 2 to buy that one. Maybe that changed the status of part 3 somehow???