Lesson 1DE32 Acquiring Institution Identification Code: format (LLVAR up to 11n), use in routing and acquiring identificationDescribes DE32 LLVAR numeric format and how acquirer identifiers are assigned. Explains routing to the correct acquirer host, multi-acquirer setups, and how DE32 interacts with network-specific routing tables.
LLVAR format and numeric constraintsAcquirer ID assignment and governanceUse of DE32 in network routingMulti-acquirer and aggregator modelsLogging DE32 for settlement mappingLesson 2DE41 Card Acceptor Terminal Identification: format (8an), terminal routing and loggingExplains DE41 format, uniqueness rules, and how terminals are identified across merchants and locations. Covers routing, monitoring, fraud analysis, and how terminal IDs interact with merchant and store hierarchies.
8an format and allowed charactersTerminal ID uniqueness strategiesTerminal ID in routing and profilesTerminal ID in fraud and risk rulesTerminal inventory and lifecycle useLesson 3DE2 Primary Account Number (PAN): field name, format (LLVAR up to 19 numeric), and role in routing/BIN lookupDetails DE2 structure, PAN length rules, and LLVAR encoding. Explains BIN ranges, routing decisions, and how PAN drives scheme, product, and issuer identification while respecting masking and PCI constraints in logs.
LLVAR encoding and PAN length limitsBIN ranges and issuer identificationPAN role in network routing decisionsPAN validation and Luhn check usageMasking PAN in logs and PCI impactsLesson 4DE38 Authorisation Identification Response: format (6an), issuing bank authorisation code and audit useExplains DE38 structure, allowed characters, and how issuers generate authorisation codes. Covers use in host logs, acquirer records, and dispute workflows, plus consistency rules between request and response messages.
Format 6an and character constraintsIssuer code generation strategiesMapping DE38 across request/responseUse in acquirer and issuer audit logsRole in chargeback and dispute researchLesson 5DE3 Processing Code: format (6n), meaning segments (transaction type, account type), and role in transaction routingExplains DE3 structure, including transaction type, from and to account codes. Shows how processing code drives routing, fee logic, and authorisation rules for purchase, cash, reversal, and adjustment flows.
6n layout and segment meaningsCommon purchase and cash codesAccount selection and subaccount useRouting and fee rule determinationReversal and adjustment processingLesson 6DE39 Response Code: format (2an), interpretation rules and common response valuesExplains DE39 format, common response values, and mapping to business outcomes. Covers issuer and network responsibilities, decline versus referral handling, and how acquirers interpret ambiguous codes.
2an format and value rangesCommon approval and decline codesSoft declines and retry guidanceIssuer versus network generated codesMapping codes to merchant messagesLesson 7DE37 Retrieval Reference Number: format (12an), role in reconciliation, disputes, and trackingDescribes DE37 format, generation logic, and uniqueness across time and systems. Explains how RRN supports reconciliation, dispute research, and cross-network tracking of related transactions.
12an format and structure optionsRRN generation and uniquenessUse in reconciliation processesRole in chargebacks and disputesCross-network transaction trackingLesson 8DE14 Expiry Date: format (YYMM), card validation and decline triggersCovers DE14 format, validation rules, and issuer checks at authorisation time. Explains how expiry interacts with card status, fallback, and how networks and acquirers handle near-expiry cards.
YYMM format and parsing rulesIssuer validation of expiry dateExpired card decline scenariosNear-expiry and renewal handlingStorage and masking in host logsLesson 9DE4 Amount, Transaction: format (12n), currency handling, and settlement implicationsDescribes DE4 format, scaling to minor units, and currency alignment with DE49. Explains how authorisation amounts affect holds, partial approvals, tips, and later clearing and settlement differences.
12n format and minor unit handlingCurrency consistency with DE49Preauthorization and hold amountsPartial approvals and tip handlingImpact on clearing and settlementLesson 10DE22 Point-of-Service Entry Mode: format (3n), values for card-present, chip, contactless, keyedCovers DE22 format and coding for magstripe, chip, contactless, and manual entry. Explains how entry mode affects risk scoring, fallback handling, liability, and issuer authorisation strategies for different channels.
3n structure and subfield meaningsCard-present versus card-not-presentChip, contactless, and fallback codingManual and key-entered transaction flagsImpact on risk, fraud, and liabilityLesson 11DE7 Transmission Date & Time: format (MMDDhhmmss), role in logging, timeouts, and reconciliationDetails DE7 format, time zone considerations, and synchronisation with host clocks. Explains its role in timeout handling, duplicate detection, reconciliation, and matching authorisations with clearing records.
MMDDhhmmss format and examplesTime zone and clock sync issuesUse in timeout and retry handlingDuplicate and late message detectionReconciliation and settlement matchingLesson 12DE49 Transaction Currency Code: format (3n, numeric ISO 4217), currency conversion and routing impactsCovers DE49 numeric ISO 4217 coding, relationship to DE4 and DE51, and how currency codes influence routing, FX conversion, and multi-currency merchant setups in authorisation flows.
3n ISO 4217 numeric codesAlignment with DE4 and DE51Multi-currency merchant scenariosFX conversion and DCC decisionsRouting based on currency fieldsLesson 13DE11 System Trace Audit Number (STAN): format (6n), uniqueness, correlation between request/responseCovers DE11 numeric format, generation rules, and uniqueness windows. Explains how STAN links requests and responses, supports traceability across systems, and interacts with RRN and internal audit keys.
6n format and rollover behaviorSTAN generation at switch or hostUniqueness windows and collisionsCorrelation of request and responseUse in monitoring and incident traces
