Amazon Connect Chat Widget - Image display and Interactive Messaging

We are trying to implement rich interactive messaging using Amazon Connect. The documentation says SendMessage API accepts application/vnd.amazonaws.connect.message.interactive.response as content type. But we could not get this working - error says the supplied json object (such as QuickReply) is not an interactive message. We tried with Application/json content type and it gives parameter validation errors.

Example implementations all show how to configure the templates with LEX. We are not using Lex for chat and instead using native calls with Connect and Participant API. Alternately we tried displaying image with Markdown using ![Image] (url) tag and it is not working either. All other markdown commands work fine.

Any help is appreciated.