Short answer: choose an SMS-first authentication messaging API with direct OTP start and verification calls when you own the login templates and need US/EU delivery; keep email as an application-managed fallback, and choose a managed multichannel verification product instead if SMTP relay, voice, WhatsApp, or managed email OTP is mandatory.
For a media marketplace, that decision has an awkward but useful boundary. The new-order notification and the seller's login code may share a communications layer, but they should not share one generic "send message" abstraction. An order alert can tolerate a delayed pull from an event timeline. A login challenge cannot pretend that delivery means verification. The evaluation constraint is therefore template ownership: who renders the code, who controls expiry and retry rules, and who records the successful challenge?
That distinction cuts through a lot of feature-page noise.
How should a beginner-friendly authentication API handle US/EU login OTP and email fallback?
A beginner-friendly API should make two states explicit: an OTP was requested, and a submitted code was verified. Direct SMS OTP calls fit that model better than treating a login code as ordinary message text. The application still owns the surrounding authentication state: which seller is attempting to sign in, how many attempts remain, when the session becomes valid, and whether a fallback is permitted.
