Integrating Cloudinary File picker widget for uploading problem in the procees

I have use this link has reference :
Integrating Cloudinary File picker widget for uploading PDF files – Yaayyyy! - Thunkable Discuss - Community

I receive unknow API Key null
I pass the API from my firebase ; I pass my cloudname !!!
The HTML firebase Hosting is like this:
HTML file from the firebaseHosting.txt (1.9 KB)

the firebase hosting send to thunkable the message “loaded”
ThunkableWebviewerExtension.postMessage(‘loaded’);//send Thunkable a ready message
to respond with UID
This loaded message is received by thunkable :

Then thunkabbe send the UID in the form : Thunkableusers/“uid”

Thunkable send then (post message) thunkableusers/uid

Can some one tell me how can i display the message in the window created by the HTML file of the firebasehosting send by thunkable. The received message by the firebase hosting HTLM is in these part of the program : ThunkableWebviewerExtension.receiveMessage(function (message) ??