Getting fake currency notes in coin vending machines led the Reserve Bank to announce the unified payment system-based alternative, Deputy Governor T Rabi Sankar said on Wednesday. Sankar said the RBI had installed coin vending machines at strategic places like vegetable markets where there is a high demand for coins but had to grapple with the challenge of fake notes. “The problem then was that the currency that was being fed into these machines was found to be very often fake … so that became an issue,” he told reporters at the central bank headquarters here.