24-hour window - rule for sending outgoing messages in WhatsApp Business API
You can communicate with the client free of charge and without any restrictions for 24 hours from the last message of the client. Not only the answer is considered as a message, but also clicking on the button in the text message.
Once the 24 hours are over, the client can only write a template message, the delivery of which is paid (there are exceptions for customer support services).
If you build the communication intelligently, this restriction does not affect the effective sales
As part of the 24-hour window after the client replies, all your messages in the dialog box with the client will be free.