R51 return code: Item Related to RCK Entry is Ineligible or RCK Entry is Improper

R51 is the return reason code Item Related to RCK Entry is Ineligible or RCK Entry is Improper. The item behind an RCK entry was ineligible, or the RCK entry was improper.

RCK (re-presented check) entries.

It is sent by the RDFI as a return entry: the original entry goes back to the ODFI with an addenda record carrying R51, and the ODFI passes the return on to the Originator.

• The check behind an RCK entry was not eligible to be re-presented through ACH, or the RCK entry itself was improper.

Extended return: available to the ODFI by opening of business on the banking day after the 60th calendar day following the settlement date of the original entry.

The extended window needs the Receiver’s Written Statement of Unauthorized Debit: a signed or similarly authenticated statement the Receiver gives the RDFI. The RDFI must have it before returning the entry and keeps it, providing a copy to the ODFI on request. Since October 1, 2024 the RDFI must also send the return by the opening of the sixth banking day after it finishes reviewing the statement, so a return can be due well before the 60 days run out.

Corporate accounts have no 60-day window for unauthorized debits: a business disputes one with R29 within 2 banking days.

• Check RCK eligibility before re-presenting a returned check electronically.
• It counts toward the Originator’s unauthorized return rate, which Nacha reviews above 0.5% of debits.

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.

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.

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/R51?set=ach-return'

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "lookup_payment_code",
    "arguments": {
      "code": "R51",
      "set": "ach-return"
    }
  }
}

{
  "code": "R51",
  "set": "ach-return",
  "found": true,
  "matches": [
    {
      "set": "ach-return",
      "code": "R51",
      "name": "Item Related to RCK Entry is Ineligible or RCK Entry is Improper",
      "description": "The item behind an RCK entry was ineligible, or the RCK entry was improper.",
      "details": {
        "category": "return",
        "timeframe": "Extended return: available to the ODFI by opening of business on the banking day after the 60th calendar day following the settlement date of the original entry",
        "timeframeKind": "calendar-days",
        "timeframeDays": 60,
        "timeframeFrom": "original-settlement",
        "account": "consumer",
        "accountNote": "RCK (re-presented check) entries.",
        "writtenStatement": true,
        "initiatedBy": "RDFI",
        "note": "RCK only",
        "effectiveFrom": null,
        "upcomingChange": null,
        "caveat": "A Written Statement of Unauthorized Debit from the Receiver is required for this extended return. Since October 1, 2024 the RDFI must also send the return by the opening of the 6th banking day after it finishes reviewing the signed statement, still inside the 60-day window; check the Rules for details and exceptions."
      }
    }
  ]
}

The deadline for a settlement date: GET /api/v1/ach/return-deadline?settlement_date=2026-11-25&code=R51 or the MCP tool ach_return_deadline.

• R50State Law Affecting RCK
• R52Stop Payment on RCK Item
• R53Item and RCK Both Presented

SEC codes involved: RCK.

All ACH return codes, R01 to R85