You don’t have permission to use internal app sharing for your app
You don't need to add a privacy policy prior to it. I would suggest checking a couple of things:
That you are an authorized uploader for internal app sharing. You can check this under development tools > internal app sharing > manage uploaders in the google play console.
That you are using one of your published application IDs in the Google Play Console. For instance, if you're trying to upload somebody else's sample app to internal app sharing in your console, you should go and change the applicationID in your build.gradle to your published application ID.
Seems like (2) is most likely your issue considering your application id is most likely not com.example.
Hope this helps!
It seems that you also need to be signed into Chrome with your developer account.
I was getting this message when logging in with multiple Google accounts (e.g. the url was https://play.google.com/console/u/3/internal-app-sharing). Logging into a new Chrome session with just my developer account has it working properly (url does not contain u/3/).