In a real world example you would be correct. This would fall under the “equity” of the accounting equation assets = liabilities + equity. The equity part can be confusing but is where many of the non obvious second entries end up.
In addition to what others have said, it’s also a tricky cold start problem to get enough car issuers, users, and merchants on board. As far as I can tell (mostly from Acquired episodes linked in a separate comment), Block with Cash app / cash app pay and Apple with Apple Pay, and maybe PayPal are the main contenders that have a shot at competing with the network effects.
Highly recommend the Acquired Visa episode and the follow up on ACQ2 for those looking to learn more about the inner workings of these networks and economics and history of interchange fees and Cashback programs. These transactions can involve up to 5 (!) parties. This comment won’t do it justice, listen to the podcasts!
I’ve been down this path, all of the APIs specifically restrict monetization of apps that interface with their API, except under very specific circumstances.
Visa and MC only take .1% of the 2.9% you are thinking of. The rest goes to the banks on either side of the transaction (one for the merchant, one for the purchaser).
They are however building more “solutions” to try and capture more of the transaction fees, but most people’s disdain for the payment rails would be better redirected at the banks in this case.
