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AC01 reason code: direct debit rejected for an incorrect IBAN

Last updated: 28 October 2026

AC01 means “incorrect IBAN”: the IBAN in the SEPA direct debit has an invalid format or is not known at the payer's bank. Formal errors such as wrong check digits can be found before you submit the file.

Code
AC01
Meaning in the rulebook
Account identifier incorrect, i.e. invalid IBAN
ISO name
Incorrect Account Number
Type of R-transaction
Reject (invalid format or unknown IBAN) or return (IBAN unknown at the bank)
Schemes
SEPA Core and SEPA B2B
Collect again?
Yes, with the correct IBAN

What AC01 means

An IBAN contains two check digits that catch many typing errors. If the check digits are wrong or the length does not fit the country, the direct debit is rejected before the debit. If the IBAN is formally correct but belongs to no account at that bank, AC01 comes as a reject or as a return after the due date.

As causes, the European Payments Council lists wrong details given by the payer, a wrong IBAN in the creditor's customer data and technical problems when the collections were created.

What the payer and the creditor see

As the payer

A rejected direct debit does not appear on your statement. The creditor will contact you because they need the correct IBAN.

As the creditor

Your bank reports the rejected direct debit with AC01, depending on the bank as a return on your statement or as a status report on the submitted file.

Creditor's bank statementAssociation current account
DateTransactionAmount EUR
3 NovSEPA direct debit collection, 214 itemsMembership fees 11/2026+8,560.00
3 NovSEPA direct debit returnMandate M-0412, membership fee 11/2026Return reason AC01 Incorrect IBAN−40.00
3 NovReturn fee−3.00
Example: how a return with AC01 can appear on the creditor's bank statement. Layout and fees differ from bank to bank.

Typical causes

  • A typo when the IBAN was entered, such as a swapped or missing character.
  • The IBAN was copied incorrectly from the mandate.
  • The IBAN is stored with the wrong member or customer.
  • A technical problem when the file was created, for example when importing from a spreadsheet.

What you can do as the payer

  1. Give the creditor your correct IBAN, preferably in writing and with the mandate reference.
  2. Check whether your IBAN is correct on the mandate.
  3. Agree whether the open amount will be collected again or paid by credit transfer.

What you can do as the creditor

  1. Compare the IBAN in your customer data with the signed mandate.
  2. If the mandate itself contains a wrong IBAN, ask the payer for the correct one and have it confirmed.
  3. Check the file before you submit it with the free SEPA file check: it recalculates the check digits of every IBAN and checks the length per country. Whether the account actually exists only the payer's bank can tell.
  4. Resubmit the collection with the correct IBAN and announce the new due date. After a reject, a one-off collection stays one-off and a recurrent one stays recurrent.

Deadlines

A reject for an invalid IBAN arrives before the debit. A return because the IBAN is unknown at the bank arrives no later than five (SEPA Core) or three (SEPA B2B) bank business days after the due date.

Related reason codes

Frequently asked questions

How do I recognise an incorrect IBAN?

By its check digits (characters 3 and 4) and its length, which is fixed per country, for example 22 characters in Germany and 27 in France. The free check recalculates both for every direct debit in your file.

The IBAN is valid, but AC01 came back anyway. Why?

A formally valid IBAN does not have to belong to an existing account, for example when it was calculated from a wrong account number. Only the payer's bank can tell.

Is AC01 the same as a rejected file?

No. AC01 concerns a single direct debit. If the bank rejects the whole file, the error is in the format, the totals or the structure of the file.

Sources