How I Reduced Login Failures by 60% — A Deep Dive Into Auth UX

January 22, 20268 min readandroid performance ux

The Problem

PhonePe's login screen had a 15% failure rate. That means roughly 1 in 7 users couldn't log in on their first attempt. At 500M+ users, that's tens of millions of frustrated people.

I was tasked with fixing it. Here's the complete journey.

Understanding the Failures

First, I instrumented every possible failure point:

OTP never received (38% of failures) — Network issues, SMS gateway delays, or incorrect phone numbers
OTP expired (24% of failures) — Users took too long to enter the code
Wrong OTP entered (19% of failures) — Typos, confusion with other OTPs
App crash during login (11% of failures) — Edge cases in the auth flow
Network timeout (8% of failures) — Slow or unstable connections

The Solutions

Fix 1: Auto-read OTP with SMS Retriever API

The biggest win. Instead of asking users to manually type a 6-digit OTP, we implemented the SMS Retriever API to auto-read and auto-fill.

val client = SmsRetriever.getClient(context)
val task = client.startSmsRetriever()
task.addOnSuccessListener {
    // Register broadcast receiver for incoming SMS
    registerReceiver(smsReceiver, intentFilter)
}

Impact: OTP-related failures dropped by 45%.

Fix 2: Graceful Retry with Exponential Backoff

Instead of showing a generic "Something went wrong" error, we implemented smart retry:

First failure: Auto-retry silently after 2 seconds
Second failure: Show "Retrying..." with a spinner
Third failure: Offer alternatives (call-based OTP, WhatsApp OTP)

Impact: Network timeout failures dropped by 60%.

Fix 3: OTP Timer Extension

Our OTP expired after 30 seconds. User research showed that 35% of users on low-end devices needed more than 30 seconds (app switching to SMS app and back was slow). We extended to 60 seconds and added a visible countdown.

Impact: OTP expiry failures dropped by 50%.

Fix 4: Phone Number Validation

We added real-time validation as the user types:

Format check (10 digits, valid prefix)
Carrier detection (show carrier name for confirmation)
Previously used numbers (auto-suggest from account history)

Impact: Wrong number submissions dropped by 70%.

Fix 5: Crash-Free Login Flow

We found 8 edge cases causing crashes:

Config change during OTP verification
Back press during API call
Dual SIM number picker dismissal
Low memory during biometric prompt

Each was fixed with proper lifecycle handling and state restoration.

Impact: Auth-related crashes went to zero.

The Design Changes

Beyond technical fixes, we redesigned the UX:

Single-screen flow — Previously, phone number and OTP were on separate screens. We combined them with a smooth transition. Fewer navigation steps = fewer drop-offs.
Trust signals — Added PhonePe's security badge, "256-bit encrypted" text, and RBI compliance notice. Users are entering sensitive info — they need reassurance.
Error messages that help — Changed "Invalid OTP" to "That code didn't match. Check your SMS and try again." Changed "Network error" to "Slow connection. We'll keep trying."
Loading states — Replaced blank screens during API calls with skeleton loaders and progress indicators. Users who see progress are 3x more patient.

The Results

After 6 weeks of incremental rollout:

Login failure rate: 15% → 6% (60% reduction)
Average login time: 28 seconds → 12 seconds
Support tickets for login issues: -73%
User satisfaction (login NPS): +22 points

Key Lessons

Instrument everything — You can't fix what you can't measure. Every failure mode needs a distinct analytics event.
Don't blame the user — "Wrong OTP" is a UX failure, not a user failure. Make it harder to fail.
Test on real conditions — Our lab testing missed issues that only appeared on 2G networks with 512MB RAM devices.
Small changes, big impact — The OTP timer change was a one-line code change that eliminated 12% of all login failures.