If merchant has
1. PoS - Tap and pay on Gpay will work with Visa cards on NFC enabled android phones. Or Samsung wallet with Samsung phones (Visa and MC)
2. No PoS but has bharatpe QR - QR scan and paying with Visa cards will work via Gpay
3. No PoS and regular QR code - No option but to use UPI only via bank or rupay cc