UPI PIN is a 4 or 6 digit number that is set by users and is used to authenticate all transactions done through UPI. 

This means that you require inserting your PIN every time you make a UPI payment.

In case you forget your UPI PIN, you can reset it using your debit card or Aadhar card details by clicking on 'Forgot UPI PIN' on the bank account details page on Pay tab. Please note that your bank account should be linked with your Aadhar card for you to reset your UPI PIN via Aadhar card details.