When mobile data is patchy, send SMS first and use WhatsApp as a second attempt. SMS rides the cellular signal, while WhatsApp needs the user to have data, the app and an active account on that number.
How the two behave
A WhatsApp code can arrive instantly for a user on Wi-Fi and sit undelivered for someone whose bundle ran out. An SMS may take longer on a congested network but does not depend on a data plan.
- SMS: broad reach, works on any handset
- WhatsApp: good for users who live in the app and have data
- Neither is guaranteed, so plan for a miss
A practical order
Start with SMS, then fall back to WhatsApp after a short timer. If your audience is mostly urban smartphone users, you can reverse that order after checking your own delivery data.
Tambua lets you set an ordered journey of up to 3 channels, with the same code across attempts.
Need OTPs that reach users across Africa? Read the API docs or get a free test key.