Kotlin 在调试设备上测试时显示 UPDATE_NOT_AVAILABLE 的应用内更新 API

I am trying to integrate the new In-App Update API but I cannot able to test it's implementation. Seems like my code is fine therefore I read the Troubleshoots and am not able to understand 2 points in this document

Make sure that the app that you are testing is signed with the same signing key as the one available from Google Play.

1. 在连接的设备上安装APK时，如何在调试模式下使用相同的签名密钥签名？

If the app you are testing doesn’t appear with an available update, check that you’ve properly set up your testing tracks.

2. Is it compulsory to release App in internal testing tracks to test implementation?

Anyway I just want to test on my device and I decremented the version code from the play store version but its showing always UPDATE_NOT_AVAILABLE.

以下是代码:-

val appUpdateInfo: Task<AppUpdateInfo> = appUpdateManager.appUpdateInfo
appUpdateInfo.addOnSuccessListener {
    if (it.updateAvailability() == UpdateAvailability.UPDATE_AVAILABLE && it.isUpdateTypeAllowed(AppUpdateType.FLEXIBLE)) {
        appUpdateManager.startUpdateFlowForResult(it, AppUpdateType.FLEXIBLE, this, 2);
    }else{
        toast("Not Available")
    }
}