SecondFactor is a cloud service for generating, sending, and verifying one-time passcodes (OTPs) for account sign-up, login, and other phone-verification workflows. Product and engineering teams integrate it through an API and SDKs for Kotlin, Swift, Dart, TypeScript, and server-side development, then manage authentication templates from a dashboard. For each OTP, its Price Intelligence Engine selects the lowest-cost eligible channel based on destination pricing and recipient eligibility. If delivery is not confirmed within eight seconds, automatic fallback tries the next eligible channel. SecondFactor supports SMS, WhatsApp, Viber, and RCS, subject to destination, recipient, and account setup. Delivery logs show the destination, channel, status, and cost for each request. The service handles OTP generation, delivery, and verification so teams can add phone verification to their applications and manage delivery across multiple channels and markets.