The difference between a normal WhatsApp Business Account and a WhatsApp Business API (WABA) Account is that WABA has 2 message types:
Session Message: Any message that is sent within 24 hrs of the last conversation (last message from the business or user) is known as Session Message. The messages from the chatbot are session messages. You can put any type of content inside the 24 hr session messaging window like promotions, surveys etc.
Template Message: A template message is a reminder or alert notification that you can send to your end users 24-hrs their last message to you. Template messages need to be approved by the Facebook term before sending it to users.
Session messages are free of cost whereas you need to pay for every template message sent from the WABA number depending on the country of the recipient. Check this article which has the details of pricing for every country: https://help.hellotars.com/en/articles/5172468-whatsapp-template-message-pricing