New Delhi, Aug. 22 -- A soundbox has become a fixture at India's small shops. Now ToneTag, a 13-year-old Bengaluru company, wants to turn the humble payment-alert device into a banking interface-and eventually a gateway to credit.

The timing matters. Unified Payments Interface (UPI) merchant payments currently carry no merchant discount rate (MDR). But a bill passed by the Lok Sabha allows the government to notify charges on specified digital-payment modes. If merchant payments begin generating fees, the device sitting on the counter could become more than a cost of acquiring a merchant.

Naffa Innovations Pvt. Ltd, the entity behind ToneTag, was founded by Kumar Abhishek and Vivek Kumar Singh. It uses sound waves as an additional way fo...