UPI doesn't work without a bank account. Additionally, its launch was preceded by the Jan Dhan Yojana [0] which pushed hundreds of millions of the poor to open bank accounts. Today most street vendors in India - including even pushcart vendors - will accept payment via UPI. It has become even more popular in the past couple of months because of Covid-19 and hygiene concerns with handling cash.

0. https://en.wikipedia.org/wiki/Pradhan_Mantri_Jan_Dhan_Yojana

Edit: added link