I'm on the final stretch in making my game but I've hit a roadblock trying to figure out how to integrate new packages and technologies into the game.

• Ads: I've imported the package, and can call LoadAd and ShowAd, however I get "Error showing Ad Unit <id>: NOT_READY - Placement <id>is not ready" I'm aware it takes a bit of time for the ad to load, so I created a coroutine that loads the ad, then loops through yield return 0 until Advertisement.IsReady() is true, then shows the loaded ad. When I do this, it's never ready.
• Achievements: I'm still stuck on the Google Play Console, specifically Configuration/Credentials/Authorization/OAuth Client. When I click "Create OAuth Client" it says it's created one, but then refreshes the dropdown box and there still isn't one. To be clear, I don't even know what this IS so I wouldn't know where to begin troubleshooting. In addition, after downloading and importing the GooglePlayGames package, I keep getting this message: "WARNING: Some conflicting dependencies were found. The following dependency versions were modified" The "list" of modified dependencies is empty, and a progress bar slowly fills, after which I can close it. However, it just opens itself again.
• IAP: I have a supporter button that allows users to donate $5, $10, or $15 to disable ads and for player skins. As far as I can tell this is working correctly (I can load the fake store and successful purchases change the game state) but I don't know if anything further needs to be done for this to actually connect to the Google Play Store, such as inputting some kind of unique ID or key for the game that would be received by Google.