How Open Banking APIs Actually Work — A Developer's Guide

You've integrated Stripe. You've wired up PayPal. You've copy-pasted card tokenisation code from Stack Overflow at 2am. But have you ever looked at what happens when a customer pays directly from their bank account — no card network, no Visa, no Mastercard — just a bank-to-bank transfer that settles in seconds? That's open banking. And if you're building for the UK market, you need to understand how it works under the hood. Not the marketing version. The API version. The Architecture in 30 Seconds Open banking in the UK follows a simple three-party model: ASPSP (Account Servicing Payment Service Provider) — the customer's bank (Barclays, Monzo, Revolut, etc.) TPP (Third Party Provider) — that's you (or the payment platform you integrate with) Open Banking Directory — the trust layer that verifies everyone is who they say they are When a customer initiates a payment, the flow looks like this: Your App → TPP (e.g. Atoa) → Open Banking API → Customer's Bank → Auth (SCA) → Payment Executed