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NFC flow and troubleshooting

This document describes the NFC handshake, security constraints, and common troubleshooting steps for developers and beta testers.

Overview

  • Roles: Writer (sender) and Reader (receiver).
  • Format: payment-request.v1 JSON payload with non-sensitive fields only.

Handshake

  1. Writer prepares payment-request.v1 payload with id and optional expiresAt (epoch seconds).
  2. Reader calls useNfc().startReading() and waits for inbound payload.
  3. On read, the app validates payload using validatePaymentRequest() which enforces expiry and replay dedupe.
  4. If valid, proceed to presentation/confirm UI. If invalid, surface mapped Spanish error copy.

Security rules

  • Forbidden fields: secret, private, seed, token, passphrase, password, privKey, keyPair.
  • Replay protection: 5-minute TTL dedupe window; duplicate requests rejected deterministically.
  • Clock skew tolerance: 30s default; configurable in validator.

Platform notes

  • iOS: Core NFC requires entitlement com.apple.developer.nfc.readersession.formats and NFCReaderUsageDescription in Info.plist. Only physical devices supported.
  • Android: Add android.permission.NFC and handle foreground dispatch. Test on Pixel and Samsung-class devices.

Troubleshooting

  • NFC Unavailable: ensure device supports NFC and app has permissions.
  • NFC Disabled: ask user to enable in OS settings.
  • Timeout: ask users to bring devices closer and retry.