To transform credit card details into an ISO 8583 message, you map the card number to Field 2 (PAN), the expiry date to Field 14 (formatted as `YYMM`), and the CVC to Field 55 or another designated field, depending on the processor. A payment gateway typically handles this transformation by formatting the data into an ISO 8583 message with the appropriate Message Type Indicator (MTI) and bitmap before sending it to the acquirer, though some may use intermediate formats like JSON/XML before converting it. If you’re working with ISO 8583, tools like IPM Kit can be useful