Collect the consumer or business account number and routing number; before sending a live debit, originate a zero-dollar prenote entry by creating a Payment Order with amount set to 0 and addenda set to identify it as a prenotification
Set the effective date to at least one business day forward for standard ACH or same business day for Same-Day ACH; the RDFI has up to three banking days following the settlement date to return a prenote if the account data is invalid
Subscribe to the payment_order.returned webhook and inspect the return code: R04 (invalid account number) and R17 (file record edit criteria) indicate a data error; R03 (no account or unable to locate) indicates account not found — remediate each by contacting the account holder for corrected information
If no return is received within three banking days after the prenote settlement date, treat the account as validated and originate the live debit entry using the same account details
Record the prenote result and validation timestamp in your account data store; re-validate with a new prenote if the account details change or if a live entry returns with an account-data error code (R02, R04) at a later date
Note that prenotes do not validate account ownership or current balance — a prenote returning cleanly confirms the routing and account number format is valid at that RDFI, not that the account belongs to your customer or has sufficient funds
Known gotchas
Prenotes confirm account number routing validity only — not ownership; a fraudster who provides someone else's valid routing and account number will pass prenote validation, meaning prenotes must be combined with identity verification for consumer debit use cases
NACHA rules require that you update your customer's account data when you receive a Notification of Change (C-code) before re-originating — failing to act on a C01, C02, or C07 NOC within six banking days of receipt can result in NACHA rule violation fines
Same-Day ACH prenotes are possible but some BaaS providers do not expose same-day prenote as a distinct option; check whether your provider's API supports explicit prenote SEC codes and same-day effective date combinations, or whether prenotes default to standard next-day settlement
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