Play store Beta Testing returning 404

I had this same issue. The reason the link is not working is because the app must be published before the link will be active. I repeat the app must be published, this does not mean there must be an APK in production. On the top right of your applications developer console page there is a drop down menu that allows you to publish the app. That link will become active immediately and your app will be available in a few hours to your testers on the Play Store.

First of all you need to create or have a Google+ community.

The process is:

• Create a new Google + community. It's required to have testers through Developer Console.
• Register this community in Google Play Developer Console
• Invite your beta testers to this community.
• Wait 8-24 hours before sharing the link
• Share the link with your testers
• Verify that your app is published for Beta Testing

If everything is right, the link should show something like: