• Keep it short — a 4–6 digit code fits one SMS segment and arrives fastest.
  • Name your app — include your brand so users know it's legitimate: "Your Acme code is 482910".
  • Set an expiry — 5–10 minutes is standard; say it in the message.
  • Don't include links in OTP messages — it trains users to click, which phishers exploit.
  • Rate-limit requests on your side to prevent abuse and control cost.
  • Use a registered Sender ID so codes deliver in countries that require pre-registration.