WhatsApp Business differentiates between conversations that are initiated by the business and conversations that are initiated by the customer.
I want to start a conversation with a customer
When initiating a conversation as a business with a customer, a template message needs to be used. This requires a pre-approved Message Template — previously referred to as a Highly Structured Message or HSM. You can submit Message Templates via the WhatsApp Template Manager on the MessageBird Dashboard.
A customer initiates a new conversation with my business
When a customer proactively reaches out to your business, a 24-hour chat window opens during which you can respond at a reduced rate — these responses are called session messages. The 24-hour window is reset every time you receive an inbound message from the customer. If the 24-hour window passes, you can restart the conversation with the customer by sending a template message.