受取人の口座は形式上は正しいですが、閉鎖されており、入金できません。
AC04 means the IBAN is structurally valid and was once a real account, but the account has since been closed. The beneficiary may have changed banks or closed the account deliberately.
Contact the beneficiary and ask for their current active account details. Update your payment records and resend once you have the new IBAN.
受取人に連絡し、現在有効な口座情報を取得してから再送してください。
Track your payment by UETR — free on Ohmyfin: SWIFT トラッカー
→ Full AC04 reference (English)