PayZapp's UPI merchant payment success rate fell from 97% to 91% in two weeks. How would you find the root cause?

Introduction

PayZapp is HDFC Bank's payments app, built with Zeta, that combines UPI, a wallet, bill payments, brand vouchers and the Pixel credit cards. The prompt says: PayZapp's UPI payment success rate for scan-and-pay merchant transactions dropped from about 97% to 91% over the last two weeks, while peer-to-peer UPI looks normal. How would you investigate? A six-point fall in success rate is severe. In UPI, every failed payment at a shop counter is a moment of embarrassment for the user, and many will simply switch to PhonePe or Google Pay on the spot. I'll approach this systematically: clarify, rule out external factors, understand the journey, break down the metric, gather data, form hypotheses, find the root cause, validate, and decide on a fix.

Step 1

Clarifying Questions (3 minutes)

• How exactly is "success rate" defined: successful transactions over initiated, or over submitted after PIN entry?

Why it matters: A drop before PIN entry points to app or QR parsing issues; after PIN entry it points to bank, NPCI or merchant-side failures. Expected answer: Successful / transactions submitted after UPI PIN entry. Impact on approach: We focus on failures after the user authorises payment.

• Is the drop across all funding sources: HDFC savings accounts, other bank accounts linked on PayZapp, and RuPay credit cards on UPI?

Why it matters: Isolates whether the issuer side is the problem. Expected answer: The drop is concentrated in payments made from RuPay credit cards on UPI and from some non-HDFC bank accounts. Impact on approach: Points us towards credit-on-UPI and remitter-bank paths.

• Did we ship any app release or backend change in the last three weeks?

Why it matters: Internal changes are the most common cause. Expected answer: A new app version with a redesigned scan-and-pay screen rolled out to 50% of Android users 16 days ago. Impact on approach: We compare by app version.

• Are other UPI apps seeing a similar drop, based on NPCI dashboards or industry chatter?

Why it matters: An ecosystem-wide issue would change our response. Expected answer: No widespread outage reported. Impact on approach: The issue is likely specific to PayZapp.