I am working to publish a private, internal release for our app in the Google Play Store. I\'m getting a message saying \"An opt-in link will be available here when you publish
For many developers, it's just a matter of time. Rolling out merely gets you to the Pending publication stage. After some time you reach the Published stage and the URL will appear.
However, for your app, it looks like this app in unpublished. You can't opt-in to unpublished apps, so the opt-in link isn't shown.
For questions like this the Developer support team are usually really good, and we do have bugs sometimes, so it is always worth asking them.