When to choose SMS
SMS remains a familiar channel where messengers are unavailable or the user expects an “SMS with a code”. In Cascade the channel is set with channel: "sms" in the POST /otp/send body, or configured as the company default. The channel must be enabled in the cabinet — otherwise the API returns a clear 422 error.
Per billing docs, SMS charges 16 tokens for successful delivery, while WhatsApp and Telegram are usually 1 token each. So for mass registrations it makes sense to offer a messenger first and leave SMS as a fallback. Marketing cost orientation — from 1 ₸; see exact terms in the cabinet.
Integration is the same: Bearer key, JSON, then /otp/verify. Do not confuse SMS verification in your product with buying virtual numbers to sign up on third-party sites — Cascade does not do that. See compare, API, WhatsApp FAQ and documentation.