When should I raise an RBI complaint for UPI

You should raise an RBI complaint for UPI if your issue isn't resolved by your bank or the National Payments Corporation of India (NPCI) first. The RBI acts as a central authority for complaints that haven't been sorted out at the first level. So, always try to resolve it with your bank or through the NPCI complaint system. If those don't work, then you can approach the RBI.