Adding functionality to JitsiMeetExternalAPI

I am trying to modify external_api.js to support one basic functionality - to get the base64 image of video content when a button is clicked on the parent. To do the same, I want to enable communication between parent (my custom page with iframe) and the iframe within it. While I was wrapping my head around all this, I found a Postis library.

I am now confused as to whether I should be using the Postis library because simple iframe.contentWindow.postMessage is not working.

Also, In general I want to understand the relation and flow between jitsi_meet ‘react’, lib-jitsi-meet, and external_api.js.

Been a week almost. I hope I get a response soon.