Cannot select license testers on play console

I have published one app on Google play store where I want to test the subscription. I have added testers under setup -> App Integrity and now the list is showing under Setup -> License testing but the checkbox is disable. I cannot select the "Testers".

What could be the reason? How can I enable it to test the subscription of the Android app?

Note: The app is developed in Flutter and I have done all those the above things not from owner account. Client has given me the access for this. Also i have followed everything mentioned on the following URLs. https://support.google.com/googleplay/android-developer/answer/6062777?hl=en https://firebase.google.com/docs/app-check/android/play-integrity-provider

There could be a few reasons why the checkbox to select testers is disabled.
Here are a few things you can check:

1. Make sure that you are logged in to the Google Play Console with the account that owns the app. Only the app owner has the permission to enable testers for the app.
2. Verify that you have completed all the necessary steps to set up licensing for your app, including adding the necessary code to your app, setting up a test account, and adding a test subscription product.
3. Double-check that you have added the testers to the correct list. In the App Integrity setup, there are two lists: one for testers and one for pre-launch report users. Make sure that you have added your testers to the correct list.
4. Ensure that you have saved your changes after adding testers to the list.

If none of the above solutions work, you can try logging out of the Google Play Console and logging back in again. If the issue persists, you can contact Google Play support for further assistance.