SWIFT ISO 15022 - Code NAFF Financial acronyms The entire acronym collection of this site is now also available offline with this new app for iPhone and iPad. Meaning Not Affirmed: Counterparty has not affirmed. Usages Message type Field number Tag MT509 (Trade Status Message) 12 24B (Reason Code) MT549 (Request for Statement/Status Advice) 17 24B (Reason)