Both Apple Card and Afterpay will be successful products in the US.
In 2018 44.6% of the US smartphone market (257 million smart phone users) used iPhone. That's a potential customer base for Apple card in the US alone of 115 million. Assuming even just 10% take-up that's a decent 12 million customers using Apple card.
https://www.statista.com/statistics/236550/percentage-of-us-population-that-own-a-iphone-smartphone/