Change Gmail account to make in-app purchase? What is the procedure to change email account which you want to use to make in-app purchase?

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I am using 2 Gmail accounts and only 1 has a credit card attached. The primary account has a credit card, the secondary does not. But my secondary account is always in the payment dialogue. The secondary account is also not the account used in Play Store app. 

I found no way to change this email.
To do so, you must install the app from the same google account from which you want to make the in-app purchase. Follow these steps,


Uninstall the app on the phone.
Go to the Play Store site in your web browser and find the app. Make sure you're logged into the website with the right account!
Install the app through the Play Store by clicking on ‘Install’ button (and selecting your phone).
Wait a minute until the app is installed on your device.
Make the in-app purchase.