There’s no way small transactions cost Apple that much. Square and Stripe charge their merchants something like 23 cents for small transactions.
Sorry wasn't clear enough the 0.99 was referring to the transaction value itself, not the fee.
Re:Apple announces Apple Card credit card
by notyourday on Monday March 25, 2019 @04:09PM
(#19486306)
which is 23% on $1.00.
Roughly $50B are spent on App Store, and even more with growing number of Subscription along with other Apple Credit Card usage. That is a potential of $100B+ transaction volume.
It will likely be another entry point for Apple Cash, sending and receiving money from friends.