Technical deep dives into payments infrastructure, ISO 8583 standards, real-time risk scoring, and software engineering by Joel Tan.https://blog.joelfatnugget.xyz/https://blog.joelfatnugget.xyz/blog/lessons-to-payment-day-1-iso8583/https://blog.joelfatnugget.xyz/blog/lessons-to-payment-day-1-iso8583/ISO 8583 standards, Message Type Indicators, Bitmaps, and history of financial transaction messaging.Mon, 20 Jul 2026 00:00:00 GMThttps://blog.joelfatnugget.xyz/blog/lessons-to-payment-day-2-four-party-model/https://blog.joelfatnugget.xyz/blog/lessons-to-payment-day-2-four-party-model/Understanding the 4 Party Model with the Ya Kun coffee analogy: Cardholder, Merchant, Acquirer, and Issuer.Tue, 21 Jul 2026 00:00:00 GMThttps://blog.joelfatnugget.xyz/blog/lessons-to-payment-day-3-message-structure/https://blog.joelfatnugget.xyz/blog/lessons-to-payment-day-3-message-structure/Message Type Indicator (MTI), Bitmaps, and Data Elements in ISO8583.Wed, 22 Jul 2026 00:00:00 GMThttps://blog.joelfatnugget.xyz/blog/lessons-to-payment-day-4-reversals-and-advice/https://blog.joelfatnugget.xyz/blog/lessons-to-payment-day-4-reversals-and-advice/Understanding the key differences between reversal requests (0400/0410) and informational advice messages (0120/0220).Thu, 23 Jul 2026 00:00:00 GMThttps://blog.joelfatnugget.xyz/blog/lessons-to-payment-day-5-pan-security/https://blog.joelfatnugget.xyz/blog/lessons-to-payment-day-5-pan-security/Exploring DE2 Primary Account Number structure, Luhn Algorithm, Magstripe vulnerability, EMV chips, and Tokenization.Fri, 24 Jul 2026 00:00:00 GMThttps://blog.joelfatnugget.xyz/blog/lessons-to-payment-day-6-amount-and-timestamp/https://blog.joelfatnugget.xyz/blog/lessons-to-payment-day-6-amount-and-timestamp/DE4 Transaction Amount limits, currency smallest units, and DE7 Transmission Date & Time fraud detection.Sat, 25 Jul 2026 00:00:00 GMThttps://blog.joelfatnugget.xyz/blog/lessons-to-payment-day-7-fraud-checks-risk-scoring/https://blog.joelfatnugget.xyz/blog/lessons-to-payment-day-7-fraud-checks-risk-scoring/Fraud detection in ISO8583 messages: Visa Advance Authorisation (VAA), Visa Risk Manager (VRM), and Mastercard Decision Intelligence.Sun, 26 Jul 2026 00:00:00 GMThttps://blog.joelfatnugget.xyz/blog/lessons-to-payment-day-8-emv-vs-magstripe/https://blog.joelfatnugget.xyz/blog/lessons-to-payment-day-8-emv-vs-magstripe/Understanding EMV microchip dynamic cryptograms, magnetic stripe skimming vulnerabilities, and the 2015 liability shift.Mon, 27 Jul 2026 00:00:00 GMThttps://blog.joelfatnugget.xyz/blog/lessons-to-payment-day-9-message-routing/https://blog.joelfatnugget.xyz/blog/lessons-to-payment-day-9-message-routing/How payment messages navigate from terminal to acquirer, scheme switch, and issuing bank.Tue, 28 Jul 2026 00:00:00 GMT