Invalid Account Number Structure
Category: Account & routing Initiated by: RDFI
Applies to (SEC scope)
ALL
camt.053 mapping
AC01 — Incorrect Account Number
Reinitiation
Restricted — permitted only within the Rules’ limits
Nacha's definition
Account number structure is not valid.
Verbatim from Nacha — ISO 20022 Guide to Mapping U.S. ACH Return Items and Notifications of Change, August 2023, Version 2.01 (Table 1, return reason codes) (return reason code table). Applies to: ALL.
How it appears in an ISO 20022 statement
Nacha's mapping guide maps R04 to camt.053 reason code AC01 (Incorrect Account Number) — ISO definition: Format of the account number specified is not correct
Return time frame
Nacha's public rule pages refer to the standard "two-day" return time frame for returns that are not extended (unauthorized) returns. The governing time limit for this code is set in the Nacha Operating Rules, which Nacha sells and which were not used here, so it is not restated.
Can the entry be reinitiated?
Nacha's reinitiation rule page says the rule "will allow reinitiations to correct administrative errors", with fields other than Company Name, Company ID and Amount modified only to the extent necessary to correct an error — so Nacha's page treats a resubmission with corrected account details as a reinitiation — within the Rules' limits and carrying the RETRY PYMT description — unless the Originator obtains a new authorization after the return, in which case Nacha does not treat the debit as a reinitiation.
get the corrected details from the Receiver, and decide deliberately whether you are reinitiating or originating a freshly authorized entry.
What an operator does next
The account number itself is malformed. Fix the data at source — the record you hold is wrong, and every entry built from it will return the same way.
PaymentBrief guidance, not Nacha text. Your ODFI's procedures and the current Nacha Operating Rules govern.
Where this comes up on PaymentBrief
Direct debit explained: ACH, SEPA, Bacs and eGIRO
Where ACH debit returns sit in the mandate and collection lifecycle, and how the return-rate thresholds bear on your ODFI relationship.
Payout and disbursement failure runbook
How a returned ACH credit is triaged — repair, reissue or escalate — and why repair and retry are different decisions.
Sources for this code
- Nacha — ISO 20022 Guide to Mapping U.S. ACH Return Items and Notifications of Change, August 2023, Version 2.01 (Table 1, return reason codes) — nacha-mapping-guide, retrieved 2026-09-06
- Nacha — rule page 'ACH Network Risk and Enforcement Topics' (unauthorized return rate threshold; reinitiation of entries) — nacha-rule-page, retrieved 2026-09-06
- US Treasury, Bureau of the Fiscal Service — Green Book, Chapter 4: Returns (return reason codes for federal ACH credits; dishonored return codes) — government-guide, retrieved 2026-09-06
- Federal Reserve Financial Services — FedGlobal ACH Payments Origination Manual, 3 August 2026 (return item code tables) — ach-operator-manual, retrieved 2026-09-06