as far as i remember you need to invite the testers into a betagroup.
when they receive the invitation they got an url which they must open. Here they can accept the betatest.
I´m not sure about the exact steps. I only did it once in 2013....
Important: Developers with personal accounts created after November 13, 2023, must meet specific testing requirements before they can make their app available on Google Play. Read
support.google.com
Step 3: Share your opt-in URL with users
After you create a test, you'll get a URL link to your app to share with your testers.
The opt-in link only shows when an app is "Published." Apps in "Draft" or "Pending publication" won't show the opt-in link.
After clicking the opt-in link, your testers will get an explanation of what it means to be a tester and a link to opt in. Each tester needs to opt in using the link.
If you're running a closed test with a Google Group or Google+ Community, users need to join the group or community before opting in to your test.
-Open google play console
-Select your app
-From the left select "Release management"
-Select "App releases"
-"Internal test" > Press "Manage"
-Then find the "Opt-in URL"
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 your app", but I don't...