Session Messages can only be started by the customer after which, you can receive and send messages freely no rules apply for a 24-hour window. After the 24-hour window has expired, you can send Template Messages that have been paid for only to send notifications or reconnect with customers. Within the 24hours of the session message, you can send and receive messages multiple times with attachments, promotional content, surveys, etc while template messages after the 24-hour window only allows you to send notifications and other approved templates and no promotional or marketing content.