I using twilio flow to create simple chatbot that sends user a whatsapp message with link to provide some details and once user has provided the required details on web page, chat bot must reply with a THANKS message.
Is there anything like postback using rest api on active execution based on which a thank you message can sent. Please have look on diagram as well.
Twilio developer evangelist here.
When you say you are using Twilio flow, I guess you are using Twilio Studio to send the messages. In this case, I don't think you can achieve what you want with Studio. You can't move an execution on with the REST API.
However, it should be fairly straightforward to send the thank you message from your application using the Twilio Messaging API instead.
What you will need to do is, when the user submits the form, in your back-end code as well as saving the data to your database, make a call to the Twilio API to send the WhatsApp message. I'm not sure what your application is built in, so I've just linked to the relevant documentation.