Payments ultimately keep the economy running, and it's in the government's best interests to make sure there is as little friction as possible here. But I'm not sure it should be free. Because there is always a cost to things. If UPI is "free" then it is being funded by the taxpayers. The problem with that is, it's not very equitable distribution of cost. People who use payments less, are funding it on behalf of people who use them a lot, who ironically are able to contribute more tax. A usage based fee is essentially a service tax which many would argue is a fairer form of taxation than fixed tax.