and will then allow you to do in-app purchases too. I have a theory that after you have done the steps above, you can then search for a regular application and install it and it should be associated with the same account. The steps above seem to force the play store to make sure it associates the game with the right account.

Open the game and you'll see you can now make in-app purchases to the right account.Find the game you want to play, and then click on the store button (normally the button would read open if it was already installed).Make sure you are logged into the correct account (on both Google Play Games and Google Play Store) you want the game to be associated with by using the hamburger menu on the top-left.Open (or download, install then open) the Google Play Games app.You do this by doing the same steps as above for checking, then afterwards you need to press the cross ('x') button in the top-right corner to remove it.Then you need to remove the game from the account that it is associated with.Now let's fix which account it is associated with: Keep switching accounts and you will eventually find which account it is associated with. If the game doesn't appear in this list, then this is the reason you are having a problem. To check which account it is, go to the play store, switch to the account you expect it to be in and then go to the 'My Apps & Games'. The problem lies with what account the downloaded and installed application is associated with. Please note this works specifically for games, but I have a theory near the end that it will then allow you install apps with the right account.

However I figure a solution to solve the problem. I was having the same problem, and all the other answers didn't solve the problem.

Google play payment method