Design Cash App (P2P Payments)
Hard · System Design · about 45 minutes
Asked at Block (Square), PayPal, Coinbase, Robinhood, Stripe, JPMorgan Chase, Visa, Capital One, Ramp, Chime, Affirm, Revolut, American Express, Rippling, Kraken.
Design a peer-to-peer payments app like Cash App or Venmo for ~50M monthly users. Users hold a balance, send money to friends instantly by username, add money from a card or bank, and cash out to their bank. Assume ~10M transfers per day; money must never be created, lost or spent twice, and fraud has to be stopped before money moves.