The customer can initiate a conversation with your business.
When a customer initiates a conversation with your business by contacting you or replying to you, a Customer Care Session is initiated. This session is a 24-hour time frame in which you can engage in rich real-time interactive conversations with your customers using session messages. During one of these sessions your message is not limited to the pre-approved Message Templates, although you can still use Message Templates within a customer care session and this will be handled as part of your MAU (Monthly Active User) count.
The customer care session ends 24 hours after the last message is sent by the end-user. After this period you will only be able to send a notification using message templates. Each time the customer sends you a message, whether this is the conversation initiating message or another reply in the conversation, the 24hour customer care session will restart. So, from the last message your customer has sent you, you have 24 hours to send custom messages, free of charge unless you exceed your MAU. To continue the conversation after the Customer Care Session ends, provided you have an active opt-in from the customer, you can send a single message template.
Customer care sessions with their limitations in messaging possibilities outside that time frame, help ensure the quality of WhatsApp as a customer care channel for customers to engage with their business.