If you'd like to change the Quick Pay buttons (to the right) in the Payment-screen this can certainly be done.
- Press the menu button (the three lines) at the top left of the checkout.
- Go into Settings, at the bottom of the list.
- Choose Customize.
- Press Buttons for Quick Pay.
You see the Quick Pay buttons you have on hand. There are four places available. Press the place you want your payment method to be. A list of possible payment methods will open. Choose the one you want.
You can see immediately that a new button has been created that reflects the payment method you chose. Press Close.
The next time you take a payment you'll see the payment method shows up as a Quick Pay button!