Sandbox test whatsapp chat:

1. Go to https://console.twilio.com/us1/develop/sms/try-it-out/whatsapp-learn
2. Get the WhatsApp number, send the code to join sandbox
3. At sandbox setting, set the api endpoint
4. When Twilio WA number receives the message, it makes a POST request to the webhook URL you set (in the sandbox settings).

POST request:

From=whatsapp%3A%2B60123456789
&To=whatsapp%3A%2B14155238886
&Body=Hello+AI
&MessageSid=SMxxxxxxxxxxxx
&NumMedia=0