Because scammers often use auto-generated IDs to commit fraud (creating accounts quickly and discarding them), legitimate random IDs can sometimes be flagged as spam by users.
Sharing a UPI ID based on your mobile number (e.g., 9876543210@upi ) can inadvertently reveal your phone number and bank to strangers. To counter this, many banking apps allow users to create additional, more "random" aliases. random upi id