Where can I learn WhatsApp chatbot development?

I am trying to create a Whatsapp bot for testing some ideas. My requirements are: 1. Chat with the bot using a predefined phone number. 2. Show a list of available menus to the user. Eg. "check request status" menu option and then ask the user to input the request id 3. Connect to a database to extract result based on the user request and send that result to the user. 4. Use Free Services and API as much as possible.

1. What are the technologies I need for these? 2. Where can I learn the required technologies?

Thanks.