Affirm co-founders, CEO Max Levchin and a16z's Alex Rampell, on 25 years inside payments, from PayPal to agentic commerce: Payments is the biggest market on earth. No niche in it is smaller than $100 billion, and the industry has barely moved in 60 years. Visa and Mastercard keep card transaction windows too tight to build anything new inside. Max still calls the plastic card the best payment interface ever built. Affirm began in a 2011 email thread in which Max and Alex agreed that the…