P2P Payments in a Large Messaging App — Design, Measurement, and Risk Plan

You are a data scientist at an at-scale messaging platform evaluating a Venmo-like peer-to-peer (P2P) payments feature.

Tasks

1. Business goal and success metrics (first 90 days)
   • State the single most important business goal (objective function) for the first 90 days.
   • List 2–3 concrete success metrics with precise definitions and units.
   • Include at least one guardrail protecting core messaging health.
2. Monetization approaches and measuring impact on ARPU
   • Propose two monetization approaches (e.g., per-transaction fee, interchange/float).
   • Describe how you would measure the causal impact on ARPU while preventing subsidy-driven volume inflation.
3. Beta rollout with network interference and leakage
   • Specify the randomization unit (user, dyad, ego-network, or geo) and the exposure definition.
   • Explain how access will be enforced when a non-assigned friend wants the feature.
   • Explain how you will estimate ITT vs TOT.
4. If an RCT is infeasible — Difference-in-Differences (DiD)
   • Write the exact DiD specification: define treatment/control, pre/post windows, the estimand, required parallel-trends checks, and clustering of standard errors.
   • Name two falsification/placebo tests.
5. Top risks and mitigations
   • List the top three risks (product, fraud/regulatory, ecosystem) with: a measurable leading indicator and a mitigation you would ship before full launch.