The app works only on Android and does not support Apple or Windows phones. Old feature phone (not smartphone) users cannot use UPI. The UPI app cannot be accessed through a dormant (inactive) bank account. If your mobile number is not registered with the bank, UPI will not function. If you try to use the app through a mobile number other than the one registered, it will not work. You cannot link a payment wallet to UPI; only bank accounts can be added. At present, the upper limit per UPI transaction is one lakh rupees.
Users can download the UPI app of their respective banks from the Play Store. As more and more banks begin offering UPI, the user base will only grow.