May I ask the specific reason of your question?
Acquirer Reference Number (ARN), is a unique number that tags a credit card transaction when it goes from the merchants bank (the acquiring bank) through the card scheme to the cardholder's bank (the issuer). This number can be used by issuing banks to trace a transaction with an acquirer. Kindly give the ARN to your credit card issuer, and you will be assisted in tracking the money.
Is it helping with your doubts?
SAP is requiring this number to be able to complete expenses. I have spent hours on the phone calling the credit card company and the endless hotel numbers and I can't find a person that knows what this number is much less where to get it. I'm out almost a 1000 dollars because I'm going to give up soon and never use my credit card again for work expenses again.