When you download an app on Google Play, it uses Google payment system by default. Even if the actual payment is done via PayPal, SMS, or any other payment method, it gets registered in Google system either way, and one cannot bypass it anyhow.
When you get registered in Google Play, a similar account on wallet.google.com is created automatically. This account has the information about all the purchases you make. Your Google mail address serves as a login, while the password matches the one for the Google account.
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