[TillE]

They're only shutting down payment for digital goods, so I'm guessing it has something to do with fraud and risk.

[jordanthoms]

Payment for digital goods is the only payment that's left from the Checkout shutdown (other than Android).

[mikeevans]

Instant Buy is for non-digital goods.

[jordanthoms]

Instant Buy doesn't actually process payments, it gives you a virtual card and then you need to use your own credit card processor.