Which return code might indicate a closed account?

The return code that indicates a closed account is R01. This specific return code is used for unauthorized transactions or cases where the account is either no longer active or has been deemed closed by the financial institution. In the context of the ACH network, when a transaction is initiated against a closed account, the receiving financial institution will return it with this code, signaling to the originating party that the account from which the funds were attempted to be withdrawn is no longer available.

Understanding the significance of return codes is vital for managing ACH transactions effectively, as they help in identifying various issues that can arise during the processing of payments. In this case, R01 directly pertains to the condition of the account, making it the correct answer for indicating a closed account.