I had to create an audit rule where the system picks up duplicates once you click save. You then have to find the duplicate and delete it from the system. Is there any other quicker ways to detect duplicates?
This sounds to me like you are asking about Invoice, not expense. This question came up in some of the classes at Fusion as well. From what I understand, there is no way to automatically see the duplicate. You do have to look for it. It is usually a simple search for that ivnoice number in the processor screen however you do need to remember that it can be in deleted or unassigned areas as well.
Do you use Concur-managed Capture? We do and it's a "rule" on their side to not pass us duplicate invoice numbers. We also have an audit rule just to make sure nothing sneaks through.