Since its inception in 2012, London-based Checkout.com has offered large businesses access to a payment gateway, fraud fighting, merchant acquiring, cross-border payout and transaction processing via a single API service. Those businesses include Adidas, Coinbase, GE Healthcare, Klarna, MoneyGram, Samsung and Wise. The company has always added new service capabilities by building technology in-house, rather than by acquisition. Its latest service—the ability to offer debit and prepaid card issuing and management—was also built in-house, including connections to the card networks, authent...