Cost

Meta charges for WhatsApp API usage based on sessions.

A session is said to have started, when a user sends a message to your WhatsApp number, or the business initiates a chat with the user by sending a template message.

Business-initiated conversations have three categories utility, authentication, and marketing. User-initiated is categorized as a service conversation, each with different rates:

Marketing	Business-initiated conversations with customers that have opted into, which may include promotions or offers, informational updates like a back-in-stock alert, or invitations for customers to respond or take action. A marketing conversation is any conversation that does not qualify as utility or authentication.
Utility	Business-initiated conversations with customers that have opted into facilitating a specific, agreed-upon request or transaction, or update to a customer about an ongoing transaction, including post-purchase notifications and recurring billing statements.
Authentication	Business-initiated conversations with customers that have opted into, enabling businesses to authenticate users with one-time passcodes (OTP), potentially at multiple steps in the login process (e.g., account verification, account recovery).
Service	Any user-initiated conversation, such as to resolve a customer enquiry.

The conversation starts when the first business message in a conversation is delivered. However, the conversation type will be defined once a message has been sent by the business with the category of the template message used.

By default, every WhatsApp API gets 1,000 free sessions each month.

Cost per session

Cost varies based on the country and type of session being used.

Business Platform Pricing | WhatsApp BusinessWhatsApp Business