Response Code
What it is
The action/result code of the request: 00 approved, 05 do not honor, 51 insufficient funds, 91 issuer unavailable…
DE 39 is the single most-read field in a response. 00 (and 10/11 for partial/VIP approvals) mean approved; everything else is a decline or error class. Visa groups declines by whether a reattempt may succeed: category 1 never (04 pick up, 14 invalid card, 41/43 lost/stolen), category 2 later (51 insufficient funds, 65, 91 issuer inoperative, 96 system malfunction), category 3 only with corrected data (54 expired card), and category 4 generic codes such as 05 do not honor, which may be reattempted within Visa’s reattempt limit. Mastercard 65 and Visa 1A are soft declines that ask for strong customer authentication.
Networks extend the base set: Visa and Mastercard each publish their own response-code tables which map onto (and beyond) the ISO values. The full searchable table lives in the Response Code Reference tool.
Example values
00Approved.05Do not honor — generic decline (Visa category 4: reattempts allowed within the limit).51Insufficient funds — Visa category 2, may succeed later.91Issuer or switch inoperative — retryable.Specification reference
Defined in ISO 8583:1987 (base). Card networks publish their own dialect tables (Visa BASE I / V.I.P., Mastercard CIS) that refine formats, lengths, and — for private-use elements — the entire layout. Always confirm against the interface specification you implement.