payments · knowledge base

Credit Card & Payment Messaging

From credit-card fundamentals to hands-on ISO 8583 / EMV message parsing. Free articles get you started; advanced deep-dives (field-by-field decoding, decline troubleshooting, clearing & reconciliation) are available to subscribers.

How Credit Cards Work: The Four-Party Model

Cardholder, merchant, issuer, acquirer — plus the card network. Who's involved in a swipe and how the money moves.

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The Transaction Lifecycle: Authorization → Clearing → Settlement

Authorization, capture, clearing, settlement, refunds and chargebacks — the differences, explained once and for all.

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Reading ISO 8583: MTI, Bitmaps & Data Elements

The lingua franca of card payments. What an MTI is, how to read the bitmap, what the 128 data elements do — practise with the parser on this site.

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ISO 8583 Field Quick Reference

DE2/3/4/11/37/39/41/43/49/55 and other high-frequency fields, each in one plain sentence — look them up while parsing.

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DE39 Response Codes: Full List

00 approved / 05 do not honor / 51 insufficient funds / 54 expired / 91 issuer down… each code's meaning, what to do, and soft-vs-hard declines.

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Reversals, Timeouts & Repeats: The ISO 8583 Failure Paths

0400 or 0420? How to fill DE90, why DE95 carries the remainder not the difference, how a retry becomes a double charge, and how a lost reversal turns into an orphaned hold — with a production checklist.

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EMV Glossary: ARQC / TVR / AIP / CVM…

The wall of chip-transaction acronyms, each in one line with its TLV tag — look them up while decoding DE55.

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Scheme Differences: Why "the Same" ISO 8583 Parses Differently

Encoding (BCD/EBCDIC), headers, bitmap count, private DE48/62/63/55 — where the scheme conventions differ.

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EMV Chip & DE55 Deep Dive: ARQC / TVR / CVM

Why chip cards are safer, what each EMV TLV tag in DE55 means, how the ARQC cryptogram is generated, and how TVR/CVM drive the authorization decision.

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daily basics

Daily Basics: One Point a Minute

New to card payments? Each piece covers one concept — read in a minute, remember in one line.

What Is a Card BIN / IIN?

The first 6–8 digits — they route the transaction to the right issuer.

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STAN vs RRN?

STAN is a same-day trace number; RRN is a cross-system tracker.

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Why No Decimal Point in Amounts?

Amounts are integers in minor units; convert using the currency's decimals.

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What Is an MCC?

A merchant's "industry ID" — drives fees, rewards and risk.

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What Is CVV / CVC / CVV2?

Card security codes; the printed CVV2 must never be stored.

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