WhattNexus
OTP SMS API Integration: Reliability Checklist for Engineers
OTP is a reliability product. Fancy dashboards do not matter if codes arrive late or twice.
Treat OTP as critical path
Login and payment verification are not marketing. Prefer routes with clear latency expectations, status codes, and delivery reports. Alert on spike in failures before customers tweet.
Idempotency and double-send
Network retries will happen. Design send calls so the same client request cannot mint two different codes for one attempt. Store request IDs and map them to provider message IDs.
Webhooks over polling
Delivery receipts should land via webhook with signature verification. Polling status endpoints is fine for debug; production should close the loop asynchronously into your auth service.
Failure codes your UX can use
Invalid number, blocked, operator timeout, and balance errors need different user messages. “SMS failed, try again” without a reason burns support capacity.
WhatsApp as complement, not sole OTP
Some products notify on WhatsApp after SMS, or offer channel choice. Keep SMS as the reliability baseline until WhatsApp OTP coverage matches your user base.
WhattNexus for OTP teams
Use WhattNexus SMS APIs for transactional send and status, keep WhatsApp modules for conversations and campaigns, and share one ops view when leadership asks about deliverability.