UPI Reference number is 12 Digit unique number which start with 9. Following are the different example of how you can find reference number.
How to find reference number on PayTM app.
Step 1: Click on Passbook option from Home Screen
Step 2: Select the Bank Account used UPI payment
Step 3: Click on the transaction you made.
Step 4: Note the 12 digit reference number start with 9.