Define success metrics for multi-device handoff flow serving power users

Problem Statement Description

You are evaluating a multi-device handoff flow used by power users who frequently move between devices while completing high-value or time-sensitive payment-related tasks. For example, a user may begin checkout, invoice payment, subscription management, or transaction approval on a desktop, then continue on a mobile device for authentication, wallet access, biometric confirmation, or final submission.

The business priority is payment reliability: users should be able to complete intended payments accurately, securely, and without losing context across devices. Because this is a metrics interview, focus on how you would define success, diagnose friction, and determine whether the handoff experience is improving payment outcomes for the right users.

Your metrics should distinguish between general engagement with the handoff feature and actual reliability of payment completion. Consider where the flow begins, what qualifies as a successful handoff, what counts as a payment failure, and how to separate product issues from bank, network, authentication, fraud, or user-abandonment causes.

The metrics framework should consider:

- The primary success metric and its exact numerator, denominator, and event boundaries

- How to define a “handoff attempt,” a “completed handoff,” and a “reliable payment completion”

- Cohorts such as power users, device pairs, payment methods, regions, platforms, transaction size, and repeat usage

- Instrumentation needed across devices to stitch sessions, users, payment intents, authentication steps, and final transaction outcomes

- Funnel metrics that capture where users drop, retry, switch devices again, or abandon payment

- Guardrail metrics for fraud, duplicate charges, latency, failed authentication, support contacts, refunds, and user trust

- Diagnostic metrics that help separate handoff UX problems from payment processor, banking, connectivity, or compliance failures

- How the metric set would support decisions such as launch readiness, experiment evaluation, prioritization, and ongoing monitoring

The goal is to define a clear, decision-useful measurement framework for assessing whether the multi-device handoff flow helps power users complete payments more reliably, while protecting user trust, operational quality, and payment safety at scale.