When you tap your card, six companies talk to each other in under two seconds. txnology lets you step through that conversation yourself — choose the players, trigger the failures, and watch every message, fee, and decline move between them.
Payments is one of the best-paid, fastest-growing corners of tech — and one of the hardest to learn from the outside. The knowledge lives in acronyms, in closed documentation, and in the heads of people who've worked at acquirers and schemes for a decade.
txnology exists to fix that. Everything here is built to take you from "I've heard of an acquirer" to "I can explain interchange, 3DS liability shift, and why an on-us transaction is cheaper" — by showing you the flow instead of describing it. If you're a student, an engineer moving into fintech, or a product manager trying to break in, you're in the right place.
The simulator isn't a video or a diagram you stare at. It's a real sequence you control, one decision at a time.
Pick the channel, card scheme, issuing bank, gateway, acquirer and merchant. Every combination — Amex closed-loop, on-us, full-stack Adyen — routes differently.
Watch the ISO 8583 message travel from cardholder to issuer and back. See the token, the ARQC, the reference numbers, and the fee charged at every single step.
Trigger a fraud block, an insufficient-funds decline, a gateway timeout. Understanding why payments fail is what separates juniors from people who get hired.
Each topic maps to something you can watch happen — and then explain in your own words.
Cardholder, merchant, acquirer, issuer — and where the scheme sits between them.
Who charges whom, why the merchant pays, and how the fee splits across the chain.
How raw card data disappears, and how a liability shift protects the merchant.
Why Amex and same-bank transactions skip steps — and cost differently.
Code 05, 51, 59, 61 — what each means and where in the flow it originates.
Why your money is "reserved" first, and when the merchant actually gets paid.
Most people learn payments from a static box-and-arrow diagram. txnology turns that diagram into something alive — you make the decisions an issuer or gateway would make, and see the consequence ripple through the chain.
New interactive breakdowns, glossary deep-dives, and simulator features — sent occasionally, never spammy.
Thanks for subscribing. New lessons are on the way.