ACH return reason code
R04 return code: Invalid Account Number Structure
The account number fails the RDFI's format checks (length, characters or check digit).
What R04 means
R04 is the return reason code Invalid Account Number Structure
. The account number fails the RDFI's format checks (length, characters or check digit).
It is sent by the RDFI as a return entry: the original entry goes back to the ODFI with an addenda record carrying R04, and the ODFI passes the return on to the Originator.
Typical causes
- The account number has the wrong length or characters for the RDFI.
- It fails the RDFI’s own account-number check digit.
- Leading zeros were dropped or added when the number was keyed or imported.
Return timeframe
Available to the ODFI by opening of business on the 2nd banking day after the settlement date of the original entry.
Banking days are the Federal Reserve’s business days: weekends and Fed holidays don’t count, so a holiday in the window pushes the deadline out by a day.
Worked example
For an entry that settled on Wednesday, November 25, 2026, the day before Thanksgiving: must be available to the ODFI by opening of business on Monday, November 30, 2026.
What the Originator can do next
- Correct the account number with the Receiver before sending again.
- It counts toward the Originator’s administrative return rate (R02, R03 and R04), which Nacha reviews above 3% of debits.
How R04 appears in a NACHA file
A return is the original entry detail record (type 6) sent back with a return transaction code — 21 or 26 for a checking account, 31 or 36 for savings (21 and 31 return a credit, 26 and 36 a debit) — the original amount, and an addenda record of type 99 that carries the reason. The batch keeps the original entry’s SEC code.
| Positions | Field | In an R04 return |
|---|---|---|
| 1 | Record Type Code | 7 (addenda) |
| 2–3 | Addenda Type Code | 99 (return) |
| 4–6 | Return Reason Code | R04 |
| 7–21 | Original Entry Trace Number | Trace number of the entry being returned |
| 22–27 | Date of Death | YYMMDD for R14 and R15; blank otherwise |
| 28–35 | Original Receiving DFI Identification | First 8 digits of the original entry’s RDFI routing number |
| 36–79 | Addenda Information | Free text from the RDFI |
| 80–94 | Trace Number | The return entry’s own trace number |
To read a return file record by record, open the file in NACHA Navigator, a free sister site that parses NACHA files in your browser without uploading them.
Look up R04 from code or an AI agent
The code table on this page is the one behind the REST API and the MCP server, so a script or an AI agent gets the same answer as JSON. No key and no account.
curl -s 'https://payopskit.com/api/v1/codes/R04?set=ach-return'{
"jsonrpc": "2.0",
"id": 1,
"method": "tools/call",
"params": {
"name": "lookup_payment_code",
"arguments": {
"code": "R04",
"set": "ach-return"
}
}
}{
"code": "R04",
"set": "ach-return",
"found": true,
"matches": [
{
"set": "ach-return",
"code": "R04",
"name": "Invalid Account Number Structure",
"description": "The account number fails the RDFI's format checks (length, characters or check digit).",
"details": {
"category": "return",
"timeframe": "Available to the ODFI by opening of business on the 2nd banking day after the settlement date of the original entry",
"timeframeKind": "banking-days",
"timeframeDays": 2,
"timeframeFrom": "original-settlement",
"account": "any",
"accountNote": null,
"writtenStatement": false,
"initiatedBy": "RDFI",
"note": null,
"effectiveFrom": null,
"upcomingChange": null,
"caveat": null
}
}
]
}The MCP server is at /mcp (Streamable HTTP, no key); the API and MCP docs show how to connect Claude, Cursor or VS Code.
The deadline for a settlement date: GET /api/v1/ach/return-deadline?settlement_date=2026-11-25&code=R04 or the MCP tool ach_return_deadline.
Source: Nacha Operating Rules, Appendix Four (Return Entries). The code’s title is the Rules’ own; the rest is this site’s plain-language summary. It is informational and not a substitute for the Rules, your ACH Operator’s schedule or your ODFI agreement.