Card checkout in 2026 is a good customer experience. One-click for returning buyers, wallets, guest flows, real-time fraud screening. The problem is not the front end. It is the economics behind it and the ways it fails. Total payment cost for e-commerce is 2-4% of revenue once you count everything: processing at 1.0-2.5%, fraud losses at 0.3-0.8%, false declines at 0.5-2.0% of revenue, expired card churn running 15-25% annual renewal failure, and chargeback operations at €8-25 per dispute. Merchants optimise the first line and ignore the other four. Three implementations, with the arithmetic. A fashion retailer, €22 million, 185,000 orders, €119 average, 42% repeat. Baseline payment cost €504,600, which is 2.3% of revenue against 8-12% net margins, so payments eat 20-25% of margin. A2A reached 3% in month one, 12% by month six, 25% at maturity. At 25%: processing down €38,500, fraud down €20,900, €16,000 in false-decline revenue recovered, chargebacks down €10,140, expired card benefit €8,000. Total €93,540 on a €9,000 build. Break-even 35 days, five-year NPV €458,000. Adoption skewed hard by segment: 32% among repeat customers, 8% among first-timers, 28% on mobile, 15% on desktop, 35% on orders above €150. A freelance services marketplace, €8.5 million, paying twice, once to collect from buyers and once to pay sellers. Baseline 3.0% of volume. Marketplaces carry 0.8% chargeback rates because "service not as described" is easy to claim and hard to fight. At 35% A2A: €32,725 processing, €5,950 payouts, €14,275 fraud, €14,620 chargebacks. €67,570 total, break-even 5.1 months. The structural win is that cryptographic authorization proof kills the "I did not authorize this" dispute, which is 60-70% of marketplace chargebacks. Sellers get paid instantly instead of waiting three days. A subscription box company, €4.2 million, 12,500 subscribers at €28 a month. Payment costs: €412,800. That is 9.8% of revenue. Processing is €58,800 of it. The other €354,000 is involuntary churn: 1,000 subscribers a year lost to failed payments, 65% of those to expired cards. 60-70% never update the card, because a failed payment is a good enough reason to quit. At 28% A2A: processing saves €10,584, involuntary churn prevention retains €70,560. Churn prevention is worth 6.7x the fee savings. Total €94,184, break-even 2.9 months. That ratio is the point. For subscriptions, payment stability beats payment cost, and it is not close. Also covered: why conversion did not drop in any of the three (flat at the retailer, up 0.2 points at the marketplace, up 0.4 at the subscription company); the honest limits, since A2A is debit-only and SEPA-bound, which still covers 85-95% of a European customer base and 70-85% of European card users who are on debit anyway; refunds landing in 10-15 seconds against 5-10 days for cards; and the optimisation details that moved the needle, like raising the bank option in the checkout list (+15% adoption) and putting bank logos next to it (+8%). Plus the competitive argument. Two €20M brands, one adopts in 2025 and one in 2027. The early mover banks €167,000 before the late mover starts, and reinvests it while the competitor is still paying full freight. For anyone who has audited their processing rate and thinks they have audited their payment costs. Full source material and the complete guide: https://go.payware.eu/p-checkout-f Produced by payware - the transaction resolution network for instant A2A payments. AI-generated from payware's published research and documentation.