If you're sending WhatsApp messages through Twilio, the billing model is different from SMS. WhatsApp charges per conversation, not per message.
A conversation is a 24-hour session between your business and a customer. Within that session, you can send unlimited messages, and the cost stays fixed.
Conversations come in four categories — Marketing, Utility, Authentication, and Service — each with its own per-conversation rate that varies by country.
Service conversations (initiated by the user within 24 hours) are typically the cheapest, while Marketing conversations are the most expensive due to opt-in and template requirements.
On top of WhatsApp's conversation fee, Twilio charges its platform fee per message. Optimizing means: prefer template-led utility flows, batch messages within a session, and design flows that encourage user-initiated conversations.
