Before sending a template, check that you have your WhatsApp Business API channel connected and templates with variables created. When you are sure everything is ready, follow the procedure:
1. Go to your ChatApp personal account.
2. Go to the "Clients" tab.
3. Click "Newsletters" in the "Work with clients" section.
4. Click on the WhatsApp Business API icon in the top right corner.
5. Click "Choose Template" and select a template with variables.
6. Fill in the variables.
7. Read how to start a newsletter and use other features in the article - How to make a mailing in WhatsApp Business API