You are providing the opportunity for users to upload a file.
Users MUST be signed in with a google account in order to upload files.
Also if you are going to do this through an AppInventor app, then you will need an extension WebViewExtra, to modify the webviewer to allow for file uploads.
It is done, Many Thanks. Just got a query in my mind, Why this specific URL require this webviewer setting, (generally other URL shown no issue of such)