Klaviyo change history: Elevated errors for SMS opt-ins, scheduling, and sending

Klaviyo reported a major incident affecting SMS subscriptions, delaying SMS sends, and causing errors creating or scheduling SMS and WhatsApp campaigns. It started at 2026-07-21 20:36 UTC and was resolved at 2026-07-21 21:09 UTC, lasting 32 min. Klaviyo implemented a fix but did not disclose the cause.