Looks like it's been out since early August.
https://www.afterpay.com/mobile-app
https://itunes.apple.com/app/afterpay/id1401019110?mt=8
Nice 18 only 5 star reviews. Ranked 180 in shopping at the moment in US.
Also available in google store, less reviews but "500+" downloads https://play.google.com/store/apps/details?id=com.afterpaymobile.us
